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 $54.55   4.652%   $57.0877   $57.09   $57.10   $57.10  
  Purchase #2 $205.69   10.279%   $226.8329   $226.83   $226.85   $226.80  
  Purchase #3 $183.83   10.742%   $203.577   $203.58   $203.60   $203.60  
  Purchase #4 $163.80   3.626%   $169.7394   $169.74   $169.75   $169.70  
  Purchase #5 $15.70   6.538%   $16.7265   $16.73   $16.75   $16.70  
  Purchase #6 $115.94   3.243%   $119.6999   $119.70   $119.70   $119.70  
  Purchase #7 $157.32   13.242%   $178.1523   $178.15   $178.15   $178.20  
  7 purchase totals = $896.83       $971.8157   $971.82   $971.90   $971.80