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 $49.45   8.337%   $53.5726   $53.57   $53.55   $53.60  
  Purchase #2 $242.47   11.736%   $270.9263   $270.93   $270.95   $270.90  
  Purchase #3 $103.56   11.686%   $115.662   $115.66   $115.65   $115.70  
  Purchase #4 $138.30   5.866%   $146.4127   $146.41   $146.40   $146.40  
  Purchase #5 $113.74   9.287%   $124.303   $124.30   $124.30   $124.30  
  Purchase #6 $93.64   4.265%   $97.6337   $97.63   $97.65   $97.60  
  Purchase #7 $134.95   8.343%   $146.2089   $146.21   $146.20   $146.20  
  7 purchase totals = $876.11       $954.7192   $954.71   $954.70   $954.70