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 $58.91   5.458%   $62.1253   $62.13   $62.15   $62.10  
  Purchase #2 $87.26   6.553%   $92.9781   $92.98   $93.00   $93.00  
  Purchase #3 $68.60   12.253%   $77.0056   $77.01   $77.00   $77.00  
  Purchase #4 $54.36   7.601%   $58.4919   $58.49   $58.50   $58.50  
  Purchase #5 $202.43   6.597%   $215.7843   $215.78   $215.80   $215.80  
  Purchase #6 $143.60   10.797%   $159.1045   $159.10   $159.10   $159.10  
  Purchase #7 $182.34   4.837%   $191.1598   $191.16   $191.15   $191.20  
  7 purchase totals = $797.50       $856.6495   $856.65   $856.70   $856.70