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 $216.49   4.239%   $225.667   $225.67   $225.65   $225.70  
  Purchase #2 $70.29   8.292%   $76.1184   $76.12   $76.10   $76.10  
  Purchase #3 $12.55   9.305%   $13.7178   $13.72   $13.70   $13.70  
  Purchase #4 $92.87   3.444%   $96.0684   $96.07   $96.05   $96.10  
  Purchase #5 $62.45   4.137%   $65.0336   $65.03   $65.05   $65.00  
  Purchase #6 $248.77   11.614%   $277.6621   $277.66   $277.65   $277.70  
  Purchase #7 $234.25   4.444%   $244.6601   $244.66   $244.65   $244.70  
  7 purchase totals = $937.67       $998.9274   $998.93   $998.85   $999.00