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 $142.76   13.311%   $161.7628   $161.76   $161.75   $161.80  
  Purchase #2 $49.98   6.757%   $53.3571   $53.36   $53.35   $53.40  
  Purchase #3 $167.79   4.777%   $175.8053   $175.81   $175.80   $175.80  
  Purchase #4 $200.55   9.555%   $219.7126   $219.71   $219.70   $219.70  
  Purchase #5 $106.42   3.552%   $110.2   $110.20   $110.20   $110.20  
  Purchase #6 $93.92   5.820%   $99.3861   $99.39   $99.40   $99.40  
  Purchase #7 $245.58   4.462%   $256.5378   $256.54   $256.55   $256.50  
  7 purchase totals = $1,007.00       $1,076.7617   $1,076.77   $1,076.75   $1,076.80