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 $85.54   8.753%   $93.0273   $93.03   $93.05   $93.00  
  Purchase #2 $72.87   3.720%   $75.5808   $75.58   $75.60   $75.60  
  Purchase #3 $54.50   12.353%   $61.2324   $61.23   $61.25   $61.20  
  Purchase #4 $236.65   10.435%   $261.3444   $261.34   $261.35   $261.30  
  Purchase #5 $141.94   13.641%   $161.302   $161.30   $161.30   $161.30  
  Purchase #6 $54.79   4.374%   $57.1865   $57.19   $57.20   $57.20  
  Purchase #7 $115.72   6.560%   $123.3112   $123.31   $123.30   $123.30  
  7 purchase totals = $762.01       $832.9846   $832.98   $833.05   $832.90