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 $199.86   13.728%   $227.2968   $227.30   $227.30   $227.30  
  Purchase #2 $106.57   6.117%   $113.0889   $113.09   $113.10   $113.10  
  Purchase #3 $238.33   12.123%   $267.2227   $267.22   $267.20   $267.20  
  Purchase #4 $109.99   13.874%   $125.25   $125.25   $125.25   $125.30  
  Purchase #5 $29.75   5.689%   $31.4425   $31.44   $31.45   $31.40  
  Purchase #6 $59.26   3.290%   $61.2097   $61.21   $61.20   $61.20  
  Purchase #7 $25.49   11.788%   $28.4948   $28.49   $28.50   $28.50  
  7 purchase totals = $769.25       $854.0054   $854.00   $854.00   $854.00