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 $213.28   6.231%   $226.5695   $226.57   $226.55   $226.60  
  Purchase #2 $160.78   7.749%   $173.2388   $173.24   $173.25   $173.20  
  Purchase #3 $91.42   5.541%   $96.4856   $96.49   $96.50   $96.50  
  Purchase #4 $169.48   8.427%   $183.7621   $183.76   $183.75   $183.80  
  Purchase #5 $177.62   4.705%   $185.977   $185.98   $186.00   $186.00  
  Purchase #6 $97.56   7.374%   $104.7541   $104.75   $104.75   $104.80  
  Purchase #7 $47.50   6.452%   $50.5647   $50.56   $50.55   $50.60  
  7 purchase totals = $957.64       $1,021.3518   $1,021.35   $1,021.35   $1,021.50