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 $90.87   5.683%   $96.0341   $96.03   $96.05   $96.00  
  Purchase #2 $146.60   8.468%   $159.0141   $159.01   $159.00   $159.00  
  Purchase #3 $58.90   3.601%   $61.021   $61.02   $61.00   $61.00  
  Purchase #4 $76.64   7.635%   $82.4915   $82.49   $82.50   $82.50  
  Purchase #5 $218.58   4.448%   $228.3024   $228.30   $228.30   $228.30  
  Purchase #6 $149.98   11.636%   $167.4317   $167.43   $167.45   $167.40  
  Purchase #7 $88.68   9.464%   $97.0727   $97.07   $97.05   $97.10  
  7 purchase totals = $830.25       $891.3675   $891.35   $891.35   $891.30