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 $193.29   13.662%   $219.6973   $219.70   $219.70   $219.70  
  Purchase #2 $146.85   6.747%   $156.758   $156.76   $156.75   $156.80  
  Purchase #3 $60.93   7.365%   $65.4175   $65.42   $65.40   $65.40  
  Purchase #4 $135.31   4.117%   $140.8807   $140.88   $140.90   $140.90  
  Purchase #5 $195.85   3.388%   $202.4854   $202.49   $202.50   $202.50  
  Purchase #6 $57.93   7.757%   $62.4236   $62.42   $62.40   $62.40  
  Purchase #7 $153.86   12.839%   $173.6141   $173.61   $173.60   $173.60  
  7 purchase totals = $944.02       $1,021.2766   $1,021.28   $1,021.25   $1,021.30