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 $124.66   13.611%   $141.6275   $141.63   $141.65   $141.60  
  Purchase #2 $34.32   5.471%   $36.1976   $36.20   $36.20   $36.20  
  Purchase #3 $54.42   12.312%   $61.1202   $61.12   $61.10   $61.10  
  Purchase #4 $200.69   9.716%   $220.189   $220.19   $220.20   $220.20  
  Purchase #5 $236.82   4.468%   $247.4011   $247.40   $247.40   $247.40  
  Purchase #6 $199.33   9.810%   $218.8843   $218.88   $218.90   $218.90  
  Purchase #7 $240.71   10.725%   $266.5261   $266.53   $266.55   $266.50  
  7 purchase totals = $1,090.95       $1,191.9458   $1,191.95   $1,192.00   $1,191.90