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 $56.67   11.741%   $63.3236   $63.32   $63.30   $63.30  
  Purchase #2 $97.68   6.199%   $103.7352   $103.74   $103.75   $103.70  
  Purchase #3 $77.85   8.803%   $84.7031   $84.70   $84.70   $84.70  
  Purchase #4 $235.80   7.186%   $252.7446   $252.74   $252.75   $252.70  
  Purchase #5 $52.38   11.378%   $58.3398   $58.34   $58.35   $58.30  
  Purchase #6 $244.60   4.473%   $255.541   $255.54   $255.55   $255.50  
  Purchase #7 $134.57   11.349%   $149.8423   $149.84   $149.85   $149.80  
  7 purchase totals = $899.55       $968.2296   $968.22   $968.25   $968.00