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 $88.26   5.468%   $93.0861   $93.09   $93.10   $93.10  
  Purchase #2 $152.44   8.347%   $165.1642   $165.16   $165.15   $165.20  
  Purchase #3 $98.47   10.193%   $108.507   $108.51   $108.50   $108.50  
  Purchase #4 $229.67   9.867%   $252.3315   $252.33   $252.35   $252.30  
  Purchase #5 $132.74   5.103%   $139.5137   $139.51   $139.50   $139.50  
  Purchase #6 $152.60   7.865%   $164.602   $164.60   $164.60   $164.60  
  Purchase #7 $242.96   11.707%   $271.4033   $271.40   $271.40   $271.40  
  7 purchase totals = $1,097.14       $1,194.6078   $1,194.60   $1,194.60   $1,194.60