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 $118.75   6.226%   $126.1434   $126.14   $126.15   $126.10  
  Purchase #2 $106.29   7.594%   $114.3617   $114.36   $114.35   $114.40  
  Purchase #3 $89.55   5.187%   $94.195   $94.20   $94.20   $94.20  
  Purchase #4 $64.94   3.660%   $67.3168   $67.32   $67.30   $67.30  
  Purchase #5 $124.56   3.118%   $128.4438   $128.44   $128.45   $128.40  
  Purchase #6 $168.56   6.205%   $179.0191   $179.02   $179.00   $179.00  
  Purchase #7 $246.39   12.407%   $276.9596   $276.96   $276.95   $277.00  
  7 purchase totals = $919.04       $986.4394   $986.44   $986.40   $986.40