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 $68.45   3.213%   $70.6493   $70.65   $70.65   $70.60  
  Purchase #2 $121.99   12.214%   $136.8899   $136.89   $136.90   $136.90  
  Purchase #3 $243.37   3.354%   $251.5326   $251.53   $251.55   $251.50  
  Purchase #4 $62.41   3.358%   $64.5057   $64.51   $64.50   $64.50  
  Purchase #5 $37.71   13.174%   $42.6779   $42.68   $42.70   $42.70  
  Purchase #6 $61.84   6.593%   $65.9171   $65.92   $65.90   $65.90  
  Purchase #7 $60.38   3.463%   $62.471   $62.47   $62.45   $62.50  
  7 purchase totals = $656.15       $694.6435   $694.65   $694.65   $694.60