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 $91.93   6.561%   $97.9615   $97.96   $97.95   $98.00  
  Purchase #2 $168.96   3.698%   $175.2081   $175.21   $175.20   $175.20  
  Purchase #3 $168.52   8.280%   $182.4735   $182.47   $182.45   $182.50  
  Purchase #4 $233.44   11.513%   $260.3159   $260.32   $260.30   $260.30  
  Purchase #5 $122.34   5.626%   $129.2228   $129.22   $129.20   $129.20  
  Purchase #6 $130.72   4.144%   $136.137   $136.14   $136.15   $136.10  
  Purchase #7 $103.41   8.450%   $112.1481   $112.15   $112.15   $112.10  
  7 purchase totals = $1,019.32       $1,093.4669   $1,093.47   $1,093.40   $1,093.40