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 $227.37   12.131%   $254.9523   $254.95   $254.95   $255.00  
  Purchase #2 $45.51   12.778%   $51.3253   $51.33   $51.35   $51.30  
  Purchase #3 $81.62   12.745%   $92.0225   $92.02   $92.00   $92.00  
  Purchase #4 $21.97   4.397%   $22.936   $22.94   $22.95   $22.90  
  Purchase #5 $29.28   11.452%   $32.6331   $32.63   $32.65   $32.60  
  Purchase #6 $192.65   4.323%   $200.9783   $200.98   $201.00   $201.00  
  Purchase #7 $92.91   7.572%   $99.9451   $99.95   $99.95   $99.90  
  7 purchase totals = $691.31       $754.7926   $754.80   $754.85   $754.70