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 $208.46   3.283%   $215.3037   $215.30   $215.30   $215.30  
  Purchase #2 $11.76   4.500%   $12.2892   $12.29   $12.30   $12.30  
  Purchase #3 $10.26   4.576%   $10.7295   $10.73   $10.75   $10.70  
  Purchase #4 $174.35   4.178%   $181.6343   $181.63   $181.65   $181.60  
  Purchase #5 $76.62   6.394%   $81.5191   $81.52   $81.50   $81.50  
  Purchase #6 $106.67   7.443%   $114.6094   $114.61   $114.60   $114.60  
  Purchase #7 $199.79   5.327%   $210.4328   $210.43   $210.45   $210.40  
  7 purchase totals = $787.91       $826.5180   $826.51   $826.55   $826.40