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 $169.25   8.556%   $183.731   $183.73   $183.75   $183.70  
  Purchase #2 $50.76   11.552%   $56.6238   $56.62   $56.60   $56.60  
  Purchase #3 $19.92   11.803%   $22.2712   $22.27   $22.25   $22.30  
  Purchase #4 $208.52   6.558%   $222.1947   $222.19   $222.20   $222.20  
  Purchase #5 $43.26   13.473%   $49.0884   $49.09   $49.10   $49.10  
  Purchase #6 $69.32   8.406%   $75.147   $75.15   $75.15   $75.10  
  Purchase #7 $174.36   13.383%   $197.6946   $197.69   $197.70   $197.70  
  7 purchase totals = $735.39       $806.7507   $806.74   $806.75   $806.70