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 $152.72   6.740%   $163.0133   $163.01   $163.00   $163.00  
  Purchase #2 $244.71   10.793%   $271.1216   $271.12   $271.10   $271.10  
  Purchase #3 $168.49   4.388%   $175.8833   $175.88   $175.90   $175.90  
  Purchase #4 $215.32   3.242%   $222.3007   $222.30   $222.30   $222.30  
  Purchase #5 $219.72   12.514%   $247.2158   $247.22   $247.20   $247.20  
  Purchase #6 $57.84   13.626%   $65.7213   $65.72   $65.70   $65.70  
  Purchase #7 $222.34   8.823%   $241.9571   $241.96   $241.95   $242.00  
  7 purchase totals = $1,281.14       $1,387.2131   $1,387.21   $1,387.15   $1,387.20