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 $227.62   6.147%   $241.6118   $241.61   $241.60   $241.60  
  Purchase #2 $203.77   5.156%   $214.2764   $214.28   $214.30   $214.30  
  Purchase #3 $23.33   4.679%   $24.4216   $24.42   $24.40   $24.40  
  Purchase #4 $241.79   4.455%   $252.5617   $252.56   $252.55   $252.60  
  Purchase #5 $173.98   8.238%   $188.3125   $188.31   $188.30   $188.30  
  Purchase #6 $62.25   9.282%   $68.028   $68.03   $68.05   $68.00  
  Purchase #7 $82.88   9.146%   $90.4602   $90.46   $90.45   $90.50  
  7 purchase totals = $1,015.62       $1,079.6722   $1,079.67   $1,079.65   $1,079.70