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 $216.50   6.102%   $229.7108   $229.71   $229.70   $229.70  
  Purchase #2 $104.84   11.574%   $116.9742   $116.97   $116.95   $117.00  
  Purchase #3 $147.69   8.527%   $160.2835   $160.28   $160.30   $160.30  
  Purchase #4 $122.76   3.697%   $127.2984   $127.30   $127.30   $127.30  
  Purchase #5 $115.73   7.841%   $124.8044   $124.80   $124.80   $124.80  
  Purchase #6 $190.43   12.596%   $214.4166   $214.42   $214.40   $214.40  
  Purchase #7 $43.93   5.364%   $46.2864   $46.29   $46.30   $46.30  
  7 purchase totals = $941.88       $1,019.7743   $1,019.77   $1,019.75   $1,019.80