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 $212.90   10.874%   $236.0507   $236.05   $236.05   $236.10  
  Purchase #2 $182.37   12.327%   $204.8507   $204.85   $204.85   $204.90  
  Purchase #3 $34.68   5.455%   $36.5718   $36.57   $36.55   $36.60  
  Purchase #4 $57.44   4.266%   $59.8904   $59.89   $59.90   $59.90  
  Purchase #5 $229.43   6.772%   $244.967   $244.97   $244.95   $245.00  
  Purchase #6 $86.75   6.864%   $92.7045   $92.70   $92.70   $92.70  
  Purchase #7 $238.95   7.347%   $256.5057   $256.51   $256.50   $256.50  
  7 purchase totals = $1,042.52       $1,131.5408   $1,131.54   $1,131.50   $1,131.70