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 $93.41   4.847%   $97.9376   $97.94   $97.95   $97.90  
  Purchase #2 $151.64   5.484%   $159.9559   $159.96   $159.95   $160.00  
  Purchase #3 $39.72   8.197%   $42.9758   $42.98   $43.00   $43.00  
  Purchase #4 $198.78   12.449%   $223.5261   $223.53   $223.55   $223.50  
  Purchase #5 $118.96   6.271%   $126.42   $126.42   $126.40   $126.40  
  Purchase #6 $55.78   8.135%   $60.3177   $60.32   $60.30   $60.30  
  Purchase #7 $137.74   8.419%   $149.3363   $149.34   $149.35   $149.30  
  7 purchase totals = $796.03       $860.4694   $860.49   $860.50   $860.40