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 $61.57   6.357%   $65.484   $65.48   $65.50   $65.50  
  Purchase #2 $11.75   8.121%   $12.7042   $12.70   $12.70   $12.70  
  Purchase #3 $119.56   10.854%   $132.537   $132.54   $132.55   $132.50  
  Purchase #4 $155.90   6.781%   $166.4716   $166.47   $166.45   $166.50  
  Purchase #5 $188.71   8.417%   $204.5937   $204.59   $204.60   $204.60  
  Purchase #6 $76.79   9.501%   $84.0858   $84.09   $84.10   $84.10  
  Purchase #7 $95.80   12.473%   $107.7491   $107.75   $107.75   $107.70  
  7 purchase totals = $710.08       $773.6254   $773.62   $773.65   $773.60