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 $206.89   12.751%   $233.2705   $233.27   $233.25   $233.30  
  Purchase #2 $162.47   4.423%   $169.656   $169.66   $169.65   $169.70  
  Purchase #3 $182.86   3.732%   $189.6843   $189.68   $189.70   $189.70  
  Purchase #4 $116.34   8.630%   $126.3801   $126.38   $126.40   $126.40  
  Purchase #5 $11.37   4.111%   $11.8374   $11.84   $11.85   $11.80  
  Purchase #6 $129.51   8.849%   $140.9703   $140.97   $140.95   $141.00  
  Purchase #7 $184.32   11.474%   $205.4689   $205.47   $205.45   $205.50  
  7 purchase totals = $993.76       $1,077.2675   $1,077.27   $1,077.25   $1,077.40