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 $65.43   4.642%   $68.4673   $68.47   $68.45   $68.50  
  Purchase #2 $44.56   7.460%   $47.8842   $47.88   $47.90   $47.90  
  Purchase #3 $85.37   3.277%   $88.1676   $88.17   $88.15   $88.20  
  Purchase #4 $34.61   6.244%   $36.771   $36.77   $36.75   $36.80  
  Purchase #5 $77.82   10.105%   $85.6837   $85.68   $85.70   $85.70  
  Purchase #6 $190.94   6.526%   $203.4007   $203.40   $203.40   $203.40  
  Purchase #7 $224.84   9.456%   $246.1009   $246.10   $246.10   $246.10  
  7 purchase totals = $723.57       $776.4754   $776.47   $776.45   $776.60