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 $38.54   13.337%   $43.6801   $43.68   $43.70   $43.70  
  Purchase #2 $156.62   8.307%   $169.6304   $169.63   $169.65   $169.60  
  Purchase #3 $177.82   3.264%   $183.624   $183.62   $183.60   $183.60  
  Purchase #4 $61.38   9.314%   $67.0969   $67.10   $67.10   $67.10  
  Purchase #5 $138.76   9.463%   $151.8909   $151.89   $151.90   $151.90  
  Purchase #6 $43.80   11.851%   $48.9907   $48.99   $49.00   $49.00  
  Purchase #7 $160.35   6.861%   $171.3516   $171.35   $171.35   $171.40  
  7 purchase totals = $777.27       $836.2646   $836.26   $836.30   $836.30