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 $192.40   9.648%   $210.9628   $210.96   $210.95   $211.00  
  Purchase #2 $190.64   4.109%   $198.4734   $198.47   $198.45   $198.50  
  Purchase #3 $6.67   4.485%   $6.9691   $6.97   $6.95   $7.00  
  Purchase #4 $172.64   8.591%   $187.4715   $187.47   $187.45   $187.50  
  Purchase #5 $219.38   9.670%   $240.594   $240.59   $240.60   $240.60  
  Purchase #6 $176.81   12.465%   $198.8494   $198.85   $198.85   $198.80  
  Purchase #7 $162.34   5.303%   $170.9489   $170.95   $170.95   $170.90  
  7 purchase totals = $1,120.88       $1,214.2691   $1,214.26   $1,214.20   $1,214.30