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 $192.46   12.187%   $215.9151   $215.92   $215.90   $215.90  
  Purchase #2 $11.45   3.157%   $11.8115   $11.81   $11.80   $11.80  
  Purchase #3 $230.72   4.646%   $241.4393   $241.44   $241.45   $241.40  
  Purchase #4 $85.79   7.722%   $92.4147   $92.41   $92.40   $92.40  
  Purchase #5 $154.32   12.522%   $173.644   $173.64   $173.65   $173.60  
  Purchase #6 $169.57   11.828%   $189.6267   $189.63   $189.65   $189.60  
  Purchase #7 $85.30   11.669%   $95.2537   $95.25   $95.25   $95.30  
  7 purchase totals = $929.61       $1,020.1050   $1,020.10   $1,020.10   $1,020.00