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 $56.51   3.650%   $58.5726   $58.57   $58.55   $58.60  
  Purchase #2 $192.30   9.313%   $210.2089   $210.21   $210.20   $210.20  
  Purchase #3 $160.87   10.485%   $177.7372   $177.74   $177.75   $177.70  
  Purchase #4 $240.75   3.513%   $249.2075   $249.21   $249.20   $249.20  
  Purchase #5 $48.36   7.685%   $52.0765   $52.08   $52.10   $52.10  
  Purchase #6 $94.46   4.856%   $99.047   $99.05   $99.05   $99.00  
  Purchase #7 $209.45   3.591%   $216.9713   $216.97   $216.95   $217.00  
  7 purchase totals = $1,002.70       $1,063.8210   $1,063.83   $1,063.80   $1,063.80