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 $38.60   8.111%   $41.7308   $41.73   $41.75   $41.70  
  Purchase #2 $116.72   6.281%   $124.0512   $124.05   $124.05   $124.10  
  Purchase #3 $219.37   12.127%   $245.973   $245.97   $245.95   $246.00  
  Purchase #4 $47.94   3.216%   $49.4818   $49.48   $49.50   $49.50  
  Purchase #5 $34.32   13.671%   $39.0119   $39.01   $39.00   $39.00  
  Purchase #6 $88.59   4.710%   $92.7626   $92.76   $92.75   $92.80  
  Purchase #7 $170.41   8.793%   $185.3942   $185.39   $185.40   $185.40  
  7 purchase totals = $715.95       $778.4055   $778.39   $778.40   $778.50