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 $129.84   10.369%   $143.3031   $143.30   $143.30   $143.30  
  Purchase #2 $109.41   4.718%   $114.572   $114.57   $114.55   $114.60  
  Purchase #3 $95.53   8.787%   $103.9242   $103.92   $103.90   $103.90  
  Purchase #4 $185.44   11.406%   $206.5913   $206.59   $206.60   $206.60  
  Purchase #5 $236.29   7.647%   $254.3591   $254.36   $254.35   $254.40  
  Purchase #6 $159.52   13.839%   $181.596   $181.60   $181.60   $181.60  
  Purchase #7 $46.62   5.181%   $49.0354   $49.04   $49.05   $49.00  
  7 purchase totals = $962.65       $1,053.3811   $1,053.38   $1,053.35   $1,053.40