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   7.595%   $66.2462   $66.25   $66.25   $66.20  
  Purchase #2 $113.35   8.413%   $122.8861   $122.89   $122.90   $122.90  
  Purchase #3 $99.71   12.677%   $112.3502   $112.35   $112.35   $112.40  
  Purchase #4 $20.64   9.741%   $22.6505   $22.65   $22.65   $22.70  
  Purchase #5 $247.43   4.654%   $258.9454   $258.95   $258.95   $258.90  
  Purchase #6 $89.85   6.363%   $95.5672   $95.57   $95.55   $95.60  
  Purchase #7 $34.47   3.685%   $35.7402   $35.74   $35.75   $35.70  
  7 purchase totals = $667.02       $714.3858   $714.40   $714.40   $714.40