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 $199.67   6.651%   $212.9501   $212.95   $212.95   $213.00  
  Purchase #2 $208.53   12.472%   $234.5379   $234.54   $234.55   $234.50  
  Purchase #3 $55.50   12.864%   $62.6395   $62.64   $62.65   $62.60  
  Purchase #4 $177.96   11.191%   $197.8755   $197.88   $197.90   $197.90  
  Purchase #5 $247.83   11.244%   $275.696   $275.70   $275.70   $275.70  
  Purchase #6 $19.88   8.498%   $21.5694   $21.57   $21.55   $21.60  
  Purchase #7 $188.53   5.246%   $198.4203   $198.42   $198.40   $198.40  
  7 purchase totals = $1,097.90       $1,203.6887   $1,203.70   $1,203.70   $1,203.70