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 $126.52   8.302%   $137.0237   $137.02   $137.00   $137.00  
  Purchase #2 $246.95   5.869%   $261.4435   $261.44   $261.45   $261.40  
  Purchase #3 $135.36   9.671%   $148.4507   $148.45   $148.45   $148.50  
  Purchase #4 $163.56   8.437%   $177.3596   $177.36   $177.35   $177.40  
  Purchase #5 $249.48   4.847%   $261.5723   $261.57   $261.55   $261.60  
  Purchase #6 $203.33   3.415%   $210.2737   $210.27   $210.25   $210.30  
  Purchase #7 $65.26   10.527%   $72.1299   $72.13   $72.15   $72.10  
  7 purchase totals = $1,190.46       $1,268.2534   $1,268.24   $1,268.20   $1,268.30