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 $232.61   11.716%   $259.8626   $259.86   $259.85   $259.90  
  Purchase #2 $134.84   12.458%   $151.6384   $151.64   $151.65   $151.60  
  Purchase #3 $130.97   4.440%   $136.7851   $136.79   $136.80   $136.80  
  Purchase #4 $167.92   11.716%   $187.5935   $187.59   $187.60   $187.60  
  Purchase #5 $165.27   12.395%   $185.7552   $185.76   $185.75   $185.80  
  Purchase #6 $148.45   12.413%   $166.8771   $166.88   $166.90   $166.90  
  Purchase #7 $38.56   7.553%   $41.4724   $41.47   $41.45   $41.50  
  7 purchase totals = $1,018.62       $1,129.9843   $1,129.99   $1,130.00   $1,130.10