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 $59.90   8.170%   $64.7938   $64.79   $64.80   $64.80  
  Purchase #2 $24.76   5.780%   $26.1911   $26.19   $26.20   $26.20  
  Purchase #3 $64.49   9.518%   $70.6282   $70.63   $70.65   $70.60  
  Purchase #4 $79.84   9.630%   $87.5286   $87.53   $87.55   $87.50  
  Purchase #5 $44.39   8.375%   $48.1077   $48.11   $48.10   $48.10  
  Purchase #6 $130.71   10.351%   $144.2398   $144.24   $144.25   $144.20  
  Purchase #7 $37.93   4.314%   $39.5663   $39.57   $39.55   $39.60  
  7 purchase totals = $442.02       $481.0555   $481.06   $481.10   $481.00