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 $169.54   8.314%   $183.6356   $183.64   $183.65   $183.60  
  Purchase #2 $72.74   6.758%   $77.6558   $77.66   $77.65   $77.70  
  Purchase #3 $149.62   7.242%   $160.4555   $160.46   $160.45   $160.50  
  Purchase #4 $204.53   12.543%   $230.1842   $230.18   $230.20   $230.20  
  Purchase #5 $65.82   5.548%   $69.4717   $69.47   $69.45   $69.50  
  Purchase #6 $50.90   9.633%   $55.8032   $55.80   $55.80   $55.80  
  Purchase #7 $13.32   8.475%   $14.4489   $14.45   $14.45   $14.40  
  7 purchase totals = $726.47       $791.6549   $791.66   $791.65   $791.70