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 $100.34   6.134%   $106.4949   $106.49   $106.50   $106.50  
  Purchase #2 $153.47   8.394%   $166.3523   $166.35   $166.35   $166.40  
  Purchase #3 $44.31   3.284%   $45.7651   $45.77   $45.75   $45.80  
  Purchase #4 $69.79   4.474%   $72.9124   $72.91   $72.90   $72.90  
  Purchase #5 $38.83   7.503%   $41.7434   $41.74   $41.75   $41.70  
  Purchase #6 $184.76   3.530%   $191.282   $191.28   $191.30   $191.30  
  Purchase #7 $102.68   6.766%   $109.6273   $109.63   $109.65   $109.60  
  7 purchase totals = $694.18       $734.1774   $734.17   $734.20   $734.20