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 $199.53   5.587%   $210.6777   $210.68   $210.70   $210.70  
  Purchase #2 $55.35   3.519%   $57.2978   $57.30   $57.30   $57.30  
  Purchase #3 $45.70   4.512%   $47.762   $47.76   $47.75   $47.80  
  Purchase #4 $221.39   4.555%   $231.4743   $231.47   $231.45   $231.50  
  Purchase #5 $225.29   11.246%   $250.6261   $250.63   $250.65   $250.60  
  Purchase #6 $23.91   11.298%   $26.6114   $26.61   $26.60   $26.60  
  Purchase #7 $185.45   7.501%   $199.3606   $199.36   $199.35   $199.40  
  7 purchase totals = $956.62       $1,023.8099   $1,023.81   $1,023.80   $1,023.90