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 $21.69   7.659%   $23.3512   $23.35   $23.35   $23.40  
  Purchase #2 $227.51   11.513%   $253.7032   $253.70   $253.70   $253.70  
  Purchase #3 $166.79   10.754%   $184.7266   $184.73   $184.75   $184.70  
  Purchase #4 $75.86   9.169%   $82.8156   $82.82   $82.80   $82.80  
  Purchase #5 $156.29   11.627%   $174.4618   $174.46   $174.45   $174.50  
  Purchase #6 $182.52   12.412%   $205.1744   $205.17   $205.15   $205.20  
  Purchase #7 $64.94   6.566%   $69.204   $69.20   $69.20   $69.20  
  7 purchase totals = $895.60       $993.4368   $993.43   $993.40   $993.50