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 $90.62   5.671%   $95.7591   $95.76   $95.75   $95.80  
  Purchase #2 $220.36   9.741%   $241.8253   $241.83   $241.85   $241.80  
  Purchase #3 $6.48   6.174%   $6.8801   $6.88   $6.90   $6.90  
  Purchase #4 $58.74   6.320%   $62.4524   $62.45   $62.45   $62.50  
  Purchase #5 $170.53   8.803%   $185.5418   $185.54   $185.55   $185.50  
  Purchase #6 $82.81   7.202%   $88.774   $88.77   $88.75   $88.80  
  Purchase #7 $226.55   7.819%   $244.2639   $244.26   $244.25   $244.30  
  7 purchase totals = $856.09       $925.4966   $925.49   $925.50   $925.60