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 $160.90   3.331%   $166.2596   $166.26   $166.25   $166.30  
  Purchase #2 $63.76   6.110%   $67.6557   $67.66   $67.65   $67.70  
  Purchase #3 $141.99   6.790%   $151.6311   $151.63   $151.65   $151.60  
  Purchase #4 $91.44   5.763%   $96.7097   $96.71   $96.70   $96.70  
  Purchase #5 $243.97   9.853%   $268.0084   $268.01   $268.00   $268.00  
  Purchase #6 $195.36   3.592%   $202.3773   $202.38   $202.40   $202.40  
  Purchase #7 $65.37   9.569%   $71.6253   $71.63   $71.65   $71.60  
  7 purchase totals = $962.79       $1,024.2671   $1,024.28   $1,024.30   $1,024.30