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 $68.59   4.297%   $71.5373   $71.54   $71.55   $71.50  
  Purchase #2 $114.58   5.813%   $121.2405   $121.24   $121.25   $121.20  
  Purchase #3 $95.36   9.393%   $104.3172   $104.32   $104.30   $104.30  
  Purchase #4 $241.97   5.371%   $254.9662   $254.97   $254.95   $255.00  
  Purchase #5 $82.63   3.250%   $85.3155   $85.32   $85.30   $85.30  
  Purchase #6 $192.63   3.179%   $198.7537   $198.75   $198.75   $198.80  
  Purchase #7 $23.64   11.647%   $26.3934   $26.39   $26.40   $26.40  
  7 purchase totals = $819.40       $862.5238   $862.53   $862.50   $862.50