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 $122.42   3.103%   $126.2187   $126.22   $126.20   $126.20  
  Purchase #2 $222.88   11.520%   $248.5558   $248.56   $248.55   $248.60  
  Purchase #3 $190.35   7.140%   $203.941   $203.94   $203.95   $203.90  
  Purchase #4 $242.90   3.655%   $251.778   $251.78   $251.80   $251.80  
  Purchase #5 $184.42   10.674%   $204.105   $204.11   $204.10   $204.10  
  Purchase #6 $123.71   8.519%   $134.2489   $134.25   $134.25   $134.20  
  Purchase #7 $38.32   13.109%   $43.3434   $43.34   $43.35   $43.30  
  7 purchase totals = $1,125.00       $1,212.1908   $1,212.20   $1,212.20   $1,212.10