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 $238.47   11.103%   $264.9473   $264.95   $264.95   $264.90  
  Purchase #2 $65.29   5.514%   $68.8901   $68.89   $68.90   $68.90  
  Purchase #3 $81.61   12.489%   $91.8023   $91.80   $91.80   $91.80  
  Purchase #4 $27.30   11.327%   $30.3923   $30.39   $30.40   $30.40  
  Purchase #5 $116.62   6.853%   $124.612   $124.61   $124.60   $124.60  
  Purchase #6 $148.29   9.825%   $162.8595   $162.86   $162.85   $162.90  
  Purchase #7 $202.31   3.223%   $208.8305   $208.83   $208.85   $208.80  
  7 purchase totals = $879.89       $952.3340   $952.33   $952.35   $952.30