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 $61.92   3.525%   $64.1027   $64.10   $64.10   $64.10  
  Purchase #2 $183.56   8.278%   $198.7551   $198.76   $198.75   $198.80  
  Purchase #3 $39.31   3.367%   $40.6336   $40.63   $40.65   $40.60  
  Purchase #4 $214.46   8.806%   $233.3453   $233.35   $233.35   $233.30  
  Purchase #5 $44.55   3.620%   $46.1627   $46.16   $46.15   $46.20  
  Purchase #6 $216.71   8.310%   $234.7186   $234.72   $234.70   $234.70  
  Purchase #7 $115.25   7.706%   $124.1312   $124.13   $124.15   $124.10  
  7 purchase totals = $875.76       $941.8492   $941.85   $941.85   $941.80