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 $226.88   9.683%   $248.8488   $248.85   $248.85   $248.80  
  Purchase #2 $154.37   13.713%   $175.5388   $175.54   $175.55   $175.50  
  Purchase #3 $169.73   12.506%   $190.9564   $190.96   $190.95   $191.00  
  Purchase #4 $40.38   13.321%   $45.759   $45.76   $45.75   $45.80  
  Purchase #5 $212.65   11.147%   $236.3541   $236.35   $236.35   $236.40  
  Purchase #6 $32.41   11.365%   $36.0934   $36.09   $36.10   $36.10  
  Purchase #7 $156.89   10.485%   $173.3399   $173.34   $173.35   $173.30  
  7 purchase totals = $993.31       $1,106.8904   $1,106.89   $1,106.90   $1,106.90