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 $144.77   13.780%   $164.7193   $164.72   $164.70   $164.70  
  Purchase #2 $86.95   9.206%   $94.9546   $94.95   $94.95   $95.00  
  Purchase #3 $207.33   12.570%   $233.3914   $233.39   $233.40   $233.40  
  Purchase #4 $36.70   7.328%   $39.3894   $39.39   $39.40   $39.40  
  Purchase #5 $207.52   9.860%   $227.9815   $227.98   $228.00   $228.00  
  Purchase #6 $247.78   13.121%   $280.2912   $280.29   $280.30   $280.30  
  Purchase #7 $197.97   6.338%   $210.5173   $210.52   $210.50   $210.50  
  7 purchase totals = $1,129.02       $1,251.2447   $1,251.24   $1,251.25   $1,251.30