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 $30.82   10.501%   $34.0564   $34.06   $34.05   $34.10  
  Purchase #2 $213.35   4.214%   $222.3406   $222.34   $222.35   $222.30  
  Purchase #3 $215.32   5.683%   $227.5566   $227.56   $227.55   $227.60  
  Purchase #4 $60.39   7.719%   $65.0515   $65.05   $65.05   $65.10  
  Purchase #5 $191.44   8.598%   $207.9   $207.90   $207.90   $207.90  
  Purchase #6 $110.68   11.786%   $123.7247   $123.72   $123.70   $123.70  
  Purchase #7 $84.90   12.698%   $95.6806   $95.68   $95.70   $95.70  
  7 purchase totals = $906.90       $976.3104   $976.31   $976.30   $976.40