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 $58.75   3.273%   $60.6729   $60.67   $60.65   $60.70  
  Purchase #2 $246.54   13.343%   $279.4358   $279.44   $279.45   $279.40  
  Purchase #3 $104.99   13.539%   $119.2046   $119.20   $119.20   $119.20  
  Purchase #4 $7.69   8.533%   $8.3462   $8.35   $8.35   $8.30  
  Purchase #5 $58.57   11.581%   $65.353   $65.35   $65.35   $65.40  
  Purchase #6 $191.81   6.584%   $204.4388   $204.44   $204.45   $204.40  
  Purchase #7 $241.35   5.840%   $255.4448   $255.44   $255.45   $255.40  
  7 purchase totals = $909.70       $992.8961   $992.89   $992.90   $992.80