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 $135.25   13.228%   $153.1409   $153.14   $153.15   $153.10  
  Purchase #2 $131.88   5.802%   $139.5317   $139.53   $139.55   $139.50  
  Purchase #3 $193.71   11.561%   $216.1048   $216.10   $216.10   $216.10  
  Purchase #4 $65.35   4.401%   $68.2261   $68.23   $68.25   $68.20  
  Purchase #5 $10.67   6.527%   $11.3664   $11.37   $11.35   $11.40  
  Purchase #6 $222.90   11.580%   $248.7118   $248.71   $248.70   $248.70  
  Purchase #7 $187.41   9.262%   $204.7679   $204.77   $204.75   $204.80  
  7 purchase totals = $947.17       $1,041.8496   $1,041.85   $1,041.85   $1,041.80