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 $194.75   7.304%   $208.9745   $208.97   $208.95   $209.00  
  Purchase #2 $5.81   3.180%   $5.9948   $5.99   $6.00   $6.00  
  Purchase #3 $130.35   9.117%   $142.234   $142.23   $142.25   $142.20  
  Purchase #4 $87.26   5.223%   $91.8176   $91.82   $91.80   $91.80  
  Purchase #5 $247.44   12.831%   $279.189   $279.19   $279.20   $279.20  
  Purchase #6 $195.57   7.676%   $210.582   $210.58   $210.60   $210.60  
  Purchase #7 $60.28   3.769%   $62.552   $62.55   $62.55   $62.60  
  7 purchase totals = $921.46       $1,001.3439   $1,001.33   $1,001.35   $1,001.40