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 $103.46   10.832%   $114.6668   $114.67   $114.65   $114.70  
  Purchase #2 $85.76   7.606%   $92.2829   $92.28   $92.30   $92.30  
  Purchase #3 $171.55   8.361%   $185.8933   $185.89   $185.90   $185.90  
  Purchase #4 $14.83   12.116%   $16.6268   $16.63   $16.65   $16.60  
  Purchase #5 $50.89   5.585%   $53.7322   $53.73   $53.75   $53.70  
  Purchase #6 $246.35   8.771%   $267.9574   $267.96   $267.95   $268.00  
  Purchase #7 $201.86   3.848%   $209.6276   $209.63   $209.65   $209.60  
  7 purchase totals = $874.70       $940.7870   $940.79   $940.85   $940.80