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 $210.29   8.226%   $227.5885   $227.59   $227.60   $227.60  
  Purchase #2 $220.56   4.590%   $230.6837   $230.68   $230.70   $230.70  
  Purchase #3 $89.92   12.576%   $101.2283   $101.23   $101.25   $101.20  
  Purchase #4 $53.42   13.769%   $60.7754   $60.78   $60.80   $60.80  
  Purchase #5 $204.99   6.244%   $217.7896   $217.79   $217.80   $217.80  
  Purchase #6 $17.55   7.551%   $18.8752   $18.88   $18.90   $18.90  
  Purchase #7 $196.70   4.759%   $206.061   $206.06   $206.05   $206.10  
  7 purchase totals = $993.43       $1,063.0017   $1,063.01   $1,063.10   $1,063.10