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 $209.29   13.126%   $236.7614   $236.76   $236.75   $236.80  
  Purchase #2 $74.39   11.816%   $83.1799   $83.18   $83.20   $83.20  
  Purchase #3 $199.36   8.761%   $216.8259   $216.83   $216.85   $216.80  
  Purchase #4 $207.64   5.288%   $218.62   $218.62   $218.60   $218.60  
  Purchase #5 $208.80   7.758%   $224.9987   $225.00   $225.00   $225.00  
  Purchase #6 $153.90   7.771%   $165.8596   $165.86   $165.85   $165.90  
  Purchase #7 $240.62   11.604%   $268.5415   $268.54   $268.55   $268.50  
  7 purchase totals = $1,294.00       $1,414.7870   $1,414.79   $1,414.80   $1,414.80