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 $187.92   12.559%   $211.5209   $211.52   $211.50   $211.50  
  Purchase #2 $29.63   12.267%   $33.2647   $33.26   $33.25   $33.30  
  Purchase #3 $55.42   5.594%   $58.5202   $58.52   $58.50   $58.50  
  Purchase #4 $62.59   11.483%   $69.7772   $69.78   $69.80   $69.80  
  Purchase #5 $26.64   5.544%   $28.1169   $28.12   $28.10   $28.10  
  Purchase #6 $226.58   10.495%   $250.3596   $250.36   $250.35   $250.40  
  Purchase #7 $119.83   13.307%   $135.7758   $135.78   $135.80   $135.80  
  7 purchase totals = $708.61       $787.3353   $787.34   $787.30   $787.40