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 $231.91   10.166%   $255.486   $255.49   $255.50   $255.50  
  Purchase #2 $150.54   13.545%   $170.9306   $170.93   $170.95   $170.90  
  Purchase #3 $219.87   6.874%   $234.9839   $234.98   $235.00   $235.00  
  Purchase #4 $239.72   10.710%   $265.394   $265.39   $265.40   $265.40  
  Purchase #5 $175.85   12.413%   $197.6783   $197.68   $197.70   $197.70  
  Purchase #6 $207.74   4.127%   $216.3134   $216.31   $216.30   $216.30  
  Purchase #7 $22.46   6.187%   $23.8496   $23.85   $23.85   $23.80  
  7 purchase totals = $1,248.09       $1,364.6358   $1,364.63   $1,364.70   $1,364.60