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 $112.81   10.126%   $124.2331   $124.23   $124.25   $124.20  
  Purchase #2 $53.81   3.478%   $55.6815   $55.68   $55.70   $55.70  
  Purchase #3 $206.62   11.599%   $230.5859   $230.59   $230.60   $230.60  
  Purchase #4 $226.89   10.455%   $250.6113   $250.61   $250.60   $250.60  
  Purchase #5 $113.51   12.197%   $127.3548   $127.35   $127.35   $127.40  
  Purchase #6 $21.65   12.781%   $24.4171   $24.42   $24.40   $24.40  
  Purchase #7 $231.25   4.161%   $240.8723   $240.87   $240.85   $240.90  
  7 purchase totals = $966.54       $1,053.7560   $1,053.75   $1,053.75   $1,053.80