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 $201.65   12.196%   $226.2432   $226.24   $226.25   $226.20  
  Purchase #2 $194.47   7.650%   $209.347   $209.35   $209.35   $209.30  
  Purchase #3 $54.71   12.778%   $61.7008   $61.70   $61.70   $61.70  
  Purchase #4 $115.88   10.132%   $127.621   $127.62   $127.60   $127.60  
  Purchase #5 $72.38   7.422%   $77.752   $77.75   $77.75   $77.80  
  Purchase #6 $126.56   6.246%   $134.4649   $134.46   $134.45   $134.50  
  Purchase #7 $171.32   7.851%   $184.7703   $184.77   $184.75   $184.80  
  7 purchase totals = $936.97       $1,021.8992   $1,021.89   $1,021.85   $1,021.90