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 $96.76   9.741%   $106.1854   $106.19   $106.20   $106.20  
  Purchase #2 $113.33   10.193%   $124.8817   $124.88   $124.90   $124.90  
  Purchase #3 $229.91   7.855%   $247.9694   $247.97   $247.95   $248.00  
  Purchase #4 $159.60   5.182%   $167.8705   $167.87   $167.85   $167.90  
  Purchase #5 $180.60   11.789%   $201.8909   $201.89   $201.90   $201.90  
  Purchase #6 $177.50   4.401%   $185.3118   $185.31   $185.30   $185.30  
  Purchase #7 $55.64   12.804%   $62.7641   $62.76   $62.75   $62.80  
  7 purchase totals = $1,013.34       $1,096.8738   $1,096.87   $1,096.85   $1,097.00