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 $246.95   10.604%   $273.1366   $273.14   $273.15   $273.10  
  Purchase #2 $69.52   4.244%   $72.4704   $72.47   $72.45   $72.50  
  Purchase #3 $6.93   8.494%   $7.5186   $7.52   $7.50   $7.50  
  Purchase #4 $169.45   9.735%   $185.946   $185.95   $185.95   $185.90  
  Purchase #5 $50.28   11.702%   $56.1638   $56.16   $56.15   $56.20  
  Purchase #6 $121.73   3.871%   $126.4422   $126.44   $126.45   $126.40  
  Purchase #7 $244.72   3.259%   $252.6954   $252.70   $252.70   $252.70  
  7 purchase totals = $909.58       $974.3730   $974.38   $974.35   $974.30