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 $142.27   12.201%   $159.6284   $159.63   $159.65   $159.60  
  Purchase #2 $238.67   4.816%   $250.1643   $250.16   $250.15   $250.20  
  Purchase #3 $213.83   12.745%   $241.0826   $241.08   $241.10   $241.10  
  Purchase #4 $147.26   7.209%   $157.876   $157.88   $157.90   $157.90  
  Purchase #5 $100.76   3.780%   $104.5687   $104.57   $104.55   $104.60  
  Purchase #6 $166.65   13.108%   $188.4945   $188.49   $188.50   $188.50  
  Purchase #7 $87.31   9.283%   $95.415   $95.42   $95.40   $95.40  
  7 purchase totals = $1,096.75       $1,197.2295   $1,197.23   $1,197.25   $1,197.30