Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $192.58   6.452%   $205.0053   $205.01   $205.00   $205.00  
  Purchase #2 $171.31   11.118%   $190.3562   $190.36   $190.35   $190.40  
  Purchase #3 $239.78   5.143%   $252.1119   $252.11   $252.10   $252.10  
  Purchase #4 $218.84   7.465%   $235.1764   $235.18   $235.20   $235.20  
  Purchase #5 $107.28   10.818%   $118.8856   $118.89   $118.90   $118.90  
  Purchase #6 $220.69   13.744%   $251.0216   $251.02   $251.00   $251.00  
  Purchase #7 $168.53   11.567%   $188.0239   $188.02   $188.00   $188.00  
  7 purchase totals = $1,319.01       $1,440.5809   $1,440.59   $1,440.55   $1,440.60