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 $235.93   13.562%   $267.9268   $267.93   $267.95   $267.90  
  Purchase #2 $48.37   6.462%   $51.4957   $51.50   $51.50   $51.50  
  Purchase #3 $211.31   6.306%   $224.6352   $224.64   $224.65   $224.60  
  Purchase #4 $91.77   7.290%   $98.46   $98.46   $98.45   $98.50  
  Purchase #5 $20.71   5.191%   $21.7851   $21.79   $21.80   $21.80  
  Purchase #6 $219.71   9.715%   $241.0548   $241.05   $241.05   $241.10  
  Purchase #7 $38.64   3.355%   $39.9364   $39.94   $39.95   $39.90  
  7 purchase totals = $866.44       $945.2940   $945.31   $945.35   $945.30