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 $54.80   11.804%   $61.2686   $61.27   $61.25   $61.30  
  Purchase #2 $216.46   8.218%   $234.2487   $234.25   $234.25   $234.20  
  Purchase #3 $69.40   10.355%   $76.5864   $76.59   $76.60   $76.60  
  Purchase #4 $166.70   7.157%   $178.6307   $178.63   $178.65   $178.60  
  Purchase #5 $141.52   10.653%   $156.5961   $156.60   $156.60   $156.60  
  Purchase #6 $149.42   11.354%   $166.3851   $166.39   $166.40   $166.40  
  Purchase #7 $185.31   10.339%   $204.4692   $204.47   $204.45   $204.50  
  7 purchase totals = $983.61       $1,078.1848   $1,078.20   $1,078.20   $1,078.20