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 $203.91   12.126%   $228.6361   $228.64   $228.65   $228.60  
  Purchase #2 $222.55   9.777%   $244.3087   $244.31   $244.30   $244.30  
  Purchase #3 $246.90   3.766%   $256.1983   $256.20   $256.20   $256.20  
  Purchase #4 $213.92   5.503%   $225.692   $225.69   $225.70   $225.70  
  Purchase #5 $155.31   8.751%   $168.9012   $168.90   $168.90   $168.90  
  Purchase #6 $33.74   3.514%   $34.9256   $34.93   $34.95   $34.90  
  Purchase #7 $44.76   10.391%   $49.411   $49.41   $49.40   $49.40  
  7 purchase totals = $1,121.09       $1,208.0729   $1,208.08   $1,208.10   $1,208.00