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 $244.44   8.864%   $266.1072   $266.11   $266.10   $266.10  
  Purchase #2 $233.92   9.159%   $255.3447   $255.34   $255.35   $255.30  
  Purchase #3 $140.28   8.766%   $152.5769   $152.58   $152.60   $152.60  
  Purchase #4 $250.48   5.117%   $263.2971   $263.30   $263.30   $263.30  
  Purchase #5 $128.93   9.454%   $141.119   $141.12   $141.10   $141.10  
  Purchase #6 $221.26   9.115%   $241.4278   $241.43   $241.45   $241.40  
  Purchase #7 $118.95   5.586%   $125.5945   $125.59   $125.60   $125.60  
  7 purchase totals = $1,338.26       $1,445.4672   $1,445.47   $1,445.50   $1,445.40