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 $139.77   11.363%   $155.6521   $155.65   $155.65   $155.70  
  Purchase #2 $233.43   4.761%   $244.5436   $244.54   $244.55   $244.50  
  Purchase #3 $35.95   9.423%   $39.3376   $39.34   $39.35   $39.30  
  Purchase #4 $177.55   5.752%   $187.7627   $187.76   $187.75   $187.80  
  Purchase #5 $186.49   5.811%   $197.3269   $197.33   $197.35   $197.30  
  Purchase #6 $206.89   9.636%   $226.8259   $226.83   $226.85   $226.80  
  Purchase #7 $191.84   9.872%   $210.7784   $210.78   $210.80   $210.80  
  7 purchase totals = $1,171.92       $1,262.2272   $1,262.23   $1,262.30   $1,262.20