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 $67.49   10.534%   $74.5994   $74.60   $74.60   $74.60  
  Purchase #2 $96.69   3.602%   $100.1728   $100.17   $100.15   $100.20  
  Purchase #3 $129.87   6.488%   $138.296   $138.30   $138.30   $138.30  
  Purchase #4 $148.34   3.805%   $153.9843   $153.98   $154.00   $154.00  
  Purchase #5 $61.35   4.236%   $63.9488   $63.95   $63.95   $63.90  
  Purchase #6 $205.41   5.549%   $216.8082   $216.81   $216.80   $216.80  
  Purchase #7 $235.88   6.167%   $250.4267   $250.43   $250.45   $250.40  
  7 purchase totals = $945.03       $998.2362   $998.24   $998.25   $998.20