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 $54.98   12.654%   $61.9372   $61.94   $61.95   $61.90  
  Purchase #2 $239.68   8.142%   $259.1947   $259.19   $259.20   $259.20  
  Purchase #3 $227.76   11.675%   $254.351   $254.35   $254.35   $254.40  
  Purchase #4 $64.99   5.426%   $68.5164   $68.52   $68.50   $68.50  
  Purchase #5 $57.28   7.357%   $61.4941   $61.49   $61.50   $61.50  
  Purchase #6 $205.99   6.585%   $219.5544   $219.55   $219.55   $219.60  
  Purchase #7 $29.66   5.200%   $31.2023   $31.20   $31.20   $31.20  
  7 purchase totals = $880.34       $956.2501   $956.24   $956.25   $956.30