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 $58.81   7.693%   $63.3343   $63.33   $63.35   $63.30  
  Purchase #2 $229.91   8.434%   $249.3006   $249.30   $249.30   $249.30  
  Purchase #3 $41.58   6.793%   $44.4045   $44.40   $44.40   $44.40  
  Purchase #4 $94.49   8.471%   $102.4942   $102.49   $102.50   $102.50  
  Purchase #5 $241.64   3.799%   $250.8199   $250.82   $250.80   $250.80  
  Purchase #6 $110.46   8.458%   $119.8027   $119.80   $119.80   $119.80  
  Purchase #7 $25.99   12.415%   $29.2167   $29.22   $29.20   $29.20  
  7 purchase totals = $802.88       $859.3729   $859.36   $859.35   $859.30