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 $133.69   10.667%   $147.9507   $147.95   $147.95   $148.00  
  Purchase #2 $236.70   10.359%   $261.2198   $261.22   $261.20   $261.20  
  Purchase #3 $62.35   7.816%   $67.2233   $67.22   $67.20   $67.20  
  Purchase #4 $48.36   12.187%   $54.2536   $54.25   $54.25   $54.30  
  Purchase #5 $23.67   7.786%   $25.5129   $25.51   $25.50   $25.50  
  Purchase #6 $247.52   6.131%   $262.6955   $262.70   $262.70   $262.70  
  Purchase #7 $123.29   10.149%   $135.8027   $135.80   $135.80   $135.80  
  7 purchase totals = $875.58       $954.6585   $954.65   $954.60   $954.70