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 $21.25   10.761%   $23.5367   $23.54   $23.55   $23.50  
  Purchase #2 $212.96   12.632%   $239.8611   $239.86   $239.85   $239.90  
  Purchase #3 $205.84   3.668%   $213.3902   $213.39   $213.40   $213.40  
  Purchase #4 $53.76   3.244%   $55.504   $55.50   $55.50   $55.50  
  Purchase #5 $140.76   5.676%   $148.7495   $148.75   $148.75   $148.70  
  Purchase #6 $200.70   9.316%   $219.3972   $219.40   $219.40   $219.40  
  Purchase #7 $203.89   11.292%   $226.9133   $226.91   $226.90   $226.90  
  7 purchase totals = $1,039.16       $1,127.3520   $1,127.35   $1,127.35   $1,127.30