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 $206.59   10.824%   $228.9513   $228.95   $228.95   $229.00  
  Purchase #2 $110.62   5.281%   $116.4618   $116.46   $116.45   $116.50  
  Purchase #3 $136.66   6.167%   $145.0878   $145.09   $145.10   $145.10  
  Purchase #4 $242.26   10.618%   $267.9832   $267.98   $268.00   $268.00  
  Purchase #5 $45.50   3.603%   $47.1394   $47.14   $47.15   $47.10  
  Purchase #6 $107.98   5.689%   $114.123   $114.12   $114.10   $114.10  
  Purchase #7 $205.77   5.520%   $217.1285   $217.13   $217.15   $217.10  
  7 purchase totals = $1,055.38       $1,136.8750   $1,136.87   $1,136.90   $1,136.90