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 $161.91   8.338%   $175.4101   $175.41   $175.40   $175.40  
  Purchase #2 $200.99   9.863%   $220.8136   $220.81   $220.80   $220.80  
  Purchase #3 $55.64   11.616%   $62.1031   $62.10   $62.10   $62.10  
  Purchase #4 $192.36   10.619%   $212.7867   $212.79   $212.80   $212.80  
  Purchase #5 $202.65   7.477%   $217.8021   $217.80   $217.80   $217.80  
  Purchase #6 $124.85   4.664%   $130.673   $130.67   $130.65   $130.70  
  Purchase #7 $63.94   5.673%   $67.5673   $67.57   $67.55   $67.60  
  7 purchase totals = $1,002.34       $1,087.1559   $1,087.15   $1,087.10   $1,087.20