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 $245.53   8.182%   $265.6193   $265.62   $265.60   $265.60  
  Purchase #2 $224.44   4.116%   $233.678   $233.68   $233.70   $233.70  
  Purchase #3 $79.84   4.858%   $83.7186   $83.72   $83.70   $83.70  
  Purchase #4 $96.58   4.737%   $101.155   $101.16   $101.15   $101.20  
  Purchase #5 $170.56   7.646%   $183.601   $183.60   $183.60   $183.60  
  Purchase #6 $67.50   5.707%   $71.3522   $71.35   $71.35   $71.40  
  Purchase #7 $59.61   8.821%   $64.8682   $64.87   $64.85   $64.90  
  7 purchase totals = $944.06       $1,003.9923   $1,004.00   $1,003.95   $1,004.10