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 $38.51   8.440%   $41.7602   $41.76   $41.75   $41.80  
  Purchase #2 $152.37   6.510%   $162.2893   $162.29   $162.30   $162.30  
  Purchase #3 $75.76   6.419%   $80.623   $80.62   $80.60   $80.60  
  Purchase #4 $194.48   11.427%   $216.7032   $216.70   $216.70   $216.70  
  Purchase #5 $151.83   7.392%   $163.0533   $163.05   $163.05   $163.10  
  Purchase #6 $22.55   9.660%   $24.7283   $24.73   $24.75   $24.70  
  Purchase #7 $210.41   12.306%   $236.3031   $236.30   $236.30   $236.30  
  7 purchase totals = $845.91       $925.4604   $925.45   $925.45   $925.50