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 $205.89   13.798%   $234.2987   $234.30   $234.30   $234.30  
  Purchase #2 $23.31   9.301%   $25.4781   $25.48   $25.50   $25.50  
  Purchase #3 $76.79   13.744%   $87.344   $87.34   $87.35   $87.30  
  Purchase #4 $52.28   11.809%   $58.4537   $58.45   $58.45   $58.50  
  Purchase #5 $140.34   12.189%   $157.446   $157.45   $157.45   $157.40  
  Purchase #6 $51.75   13.277%   $58.6208   $58.62   $58.60   $58.60  
  Purchase #7 $117.27   12.842%   $132.3298   $132.33   $132.35   $132.30  
  7 purchase totals = $667.63       $753.9711   $753.97   $754.00   $753.90