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 $223.67   10.117%   $246.2987   $246.30   $246.30   $246.30  
  Purchase #2 $183.91   12.222%   $206.3875   $206.39   $206.40   $206.40  
  Purchase #3 $155.35   12.489%   $174.7517   $174.75   $174.75   $174.80  
  Purchase #4 $238.51   3.668%   $247.2585   $247.26   $247.25   $247.30  
  Purchase #5 $20.44   11.619%   $22.8149   $22.81   $22.80   $22.80  
  Purchase #6 $142.34   12.232%   $159.751   $159.75   $159.75   $159.80  
  Purchase #7 $39.63   8.195%   $42.8777   $42.88   $42.90   $42.90  
  7 purchase totals = $1,003.85       $1,100.1400   $1,100.14   $1,100.15   $1,100.30