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 $167.61   3.634%   $173.7009   $173.70   $173.70   $173.70  
  Purchase #2 $64.91   6.389%   $69.0571   $69.06   $69.05   $69.10  
  Purchase #3 $100.36   12.278%   $112.6822   $112.68   $112.70   $112.70  
  Purchase #4 $199.29   11.190%   $221.5906   $221.59   $221.60   $221.60  
  Purchase #5 $237.96   11.707%   $265.818   $265.82   $265.80   $265.80  
  Purchase #6 $91.52   8.503%   $99.3019   $99.30   $99.30   $99.30  
  Purchase #7 $40.69   12.546%   $45.795   $45.80   $45.80   $45.80  
  7 purchase totals = $902.34       $987.9457   $987.95   $987.95   $988.00