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 $23.55   10.277%   $25.9702   $25.97   $25.95   $26.00  
  Purchase #2 $221.29   10.187%   $243.8328   $243.83   $243.85   $243.80  
  Purchase #3 $148.91   7.774%   $160.4863   $160.49   $160.50   $160.50  
  Purchase #4 $159.67   10.859%   $177.0086   $177.01   $177.00   $177.00  
  Purchase #5 $45.85   3.815%   $47.5992   $47.60   $47.60   $47.60  
  Purchase #6 $242.34   12.813%   $273.391   $273.39   $273.40   $273.40  
  Purchase #7 $27.98   9.329%   $30.5903   $30.59   $30.60   $30.60  
  7 purchase totals = $869.59       $958.8784   $958.88   $958.90   $958.90