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 $61.26   10.613%   $67.7615   $67.76   $67.75   $67.80  
  Purchase #2 $201.74   7.271%   $216.4085   $216.41   $216.40   $216.40  
  Purchase #3 $150.48   10.143%   $165.7432   $165.74   $165.75   $165.70  
  Purchase #4 $93.95   8.235%   $101.6868   $101.69   $101.70   $101.70  
  Purchase #5 $133.57   5.615%   $141.07   $141.07   $141.05   $141.10  
  Purchase #6 $241.78   13.754%   $275.0344   $275.03   $275.05   $275.00  
  Purchase #7 $240.66   10.586%   $266.1363   $266.14   $266.15   $266.10  
  7 purchase totals = $1,123.44       $1,233.8407   $1,233.84   $1,233.85   $1,233.80