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 $84.29   3.591%   $87.3169   $87.32   $87.30   $87.30  
  Purchase #2 $219.36   7.814%   $236.5008   $236.50   $236.50   $236.50  
  Purchase #3 $99.90   11.175%   $111.0638   $111.06   $111.05   $111.10  
  Purchase #4 $153.38   5.584%   $161.9447   $161.94   $161.95   $161.90  
  Purchase #5 $152.41   8.757%   $165.7565   $165.76   $165.75   $165.80  
  Purchase #6 $14.65   8.423%   $15.884   $15.88   $15.90   $15.90  
  Purchase #7 $180.83   7.829%   $194.9872   $194.99   $195.00   $195.00  
  7 purchase totals = $904.82       $973.4539   $973.45   $973.45   $973.50