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 $32.71   11.395%   $36.4373   $36.44   $36.45   $36.40  
  Purchase #2 $212.87   13.171%   $240.9071   $240.91   $240.90   $240.90  
  Purchase #3 $237.97   11.394%   $265.0843   $265.08   $265.10   $265.10  
  Purchase #4 $118.49   12.845%   $133.71   $133.71   $133.70   $133.70  
  Purchase #5 $67.61   6.703%   $72.1419   $72.14   $72.15   $72.10  
  Purchase #6 $193.62   6.456%   $206.1201   $206.12   $206.10   $206.10  
  Purchase #7 $41.32   5.707%   $43.6781   $43.68   $43.70   $43.70  
  7 purchase totals = $904.59       $998.0788   $998.08   $998.10   $998.00