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 $30.32   10.873%   $33.6167   $33.62   $33.60   $33.60  
  Purchase #2 $96.47   13.696%   $109.6825   $109.68   $109.70   $109.70  
  Purchase #3 $182.88   11.836%   $204.5257   $204.53   $204.55   $204.50  
  Purchase #4 $200.69   7.483%   $215.7076   $215.71   $215.70   $215.70  
  Purchase #5 $114.77   9.833%   $126.0553   $126.06   $126.05   $126.10  
  Purchase #6 $116.37   6.542%   $123.9829   $123.98   $124.00   $124.00  
  Purchase #7 $121.54   12.541%   $136.7823   $136.78   $136.80   $136.80  
  7 purchase totals = $863.04       $950.3530   $950.36   $950.40   $950.40