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 $118.39   6.650%   $126.2629   $126.26   $126.25   $126.30  
  Purchase #2 $93.93   9.628%   $102.9736   $102.97   $102.95   $103.00  
  Purchase #3 $123.54   11.827%   $138.1511   $138.15   $138.15   $138.20  
  Purchase #4 $204.83   4.735%   $214.5287   $214.53   $214.55   $214.50  
  Purchase #5 $231.52   6.780%   $247.2171   $247.22   $247.20   $247.20  
  Purchase #6 $55.50   13.118%   $62.7805   $62.78   $62.80   $62.80  
  Purchase #7 $119.53   3.575%   $123.8032   $123.80   $123.80   $123.80  
  7 purchase totals = $947.24       $1,015.7171   $1,015.71   $1,015.70   $1,015.80