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 $205.76   12.765%   $232.0253   $232.03   $232.05   $232.00  
  Purchase #2 $61.31   11.234%   $68.1976   $68.20   $68.20   $68.20  
  Purchase #3 $213.49   13.319%   $241.9247   $241.92   $241.90   $241.90  
  Purchase #4 $59.62   3.554%   $61.7389   $61.74   $61.75   $61.70  
  Purchase #5 $32.80   13.604%   $37.2621   $37.26   $37.25   $37.30  
  Purchase #6 $160.70   6.216%   $170.6891   $170.69   $170.70   $170.70  
  Purchase #7 $156.40   10.842%   $173.3569   $173.36   $173.35   $173.40  
  7 purchase totals = $890.08       $985.1946   $985.20   $985.20   $985.20