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 $248.87   10.513%   $275.0337   $275.03   $275.05   $275.00  
  Purchase #2 $61.60   11.494%   $68.6803   $68.68   $68.70   $68.70  
  Purchase #3 $33.30   12.705%   $37.5308   $37.53   $37.55   $37.50  
  Purchase #4 $59.80   11.514%   $66.6854   $66.69   $66.70   $66.70  
  Purchase #5 $173.45   9.600%   $190.1012   $190.10   $190.10   $190.10  
  Purchase #6 $236.41   5.148%   $248.5804   $248.58   $248.60   $248.60  
  Purchase #7 $98.90   7.806%   $106.6201   $106.62   $106.60   $106.60  
  7 purchase totals = $912.33       $993.2319   $993.23   $993.30   $993.20