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 $133.58   13.585%   $151.7268   $151.73   $151.75   $151.70  
  Purchase #2 $82.99   12.796%   $93.6094   $93.61   $93.60   $93.60  
  Purchase #3 $121.42   6.153%   $128.891   $128.89   $128.90   $128.90  
  Purchase #4 $63.66   11.153%   $70.76   $70.76   $70.75   $70.80  
  Purchase #5 $91.73   13.567%   $104.175   $104.18   $104.20   $104.20  
  Purchase #6 $164.73   7.357%   $176.8492   $176.85   $176.85   $176.80  
  Purchase #7 $41.32   6.418%   $43.9719   $43.97   $43.95   $44.00  
  7 purchase totals = $699.43       $769.9833   $769.99   $770.00   $770.00