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 $159.86   11.176%   $177.726   $177.73   $177.75   $177.70  
  Purchase #2 $127.38   3.639%   $132.0154   $132.02   $132.00   $132.00  
  Purchase #3 $149.46   9.505%   $163.6662   $163.67   $163.65   $163.70  
  Purchase #4 $177.85   11.486%   $198.2779   $198.28   $198.30   $198.30  
  Purchase #5 $193.31   10.183%   $212.9948   $212.99   $213.00   $213.00  
  Purchase #6 $223.56   10.646%   $247.3602   $247.36   $247.35   $247.40  
  Purchase #7 $8.58   6.346%   $9.1245   $9.12   $9.10   $9.10  
  7 purchase totals = $1,040.00       $1,141.1650   $1,141.17   $1,141.15   $1,141.20