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 $211.84   6.548%   $225.7113   $225.71   $225.70   $225.70  
  Purchase #2 $71.47   8.632%   $77.6393   $77.64   $77.65   $77.60  
  Purchase #3 $85.63   11.514%   $95.4894   $95.49   $95.50   $95.50  
  Purchase #4 $184.26   8.224%   $199.4135   $199.41   $199.40   $199.40  
  Purchase #5 $160.25   8.649%   $174.11   $174.11   $174.10   $174.10  
  Purchase #6 $246.26   12.427%   $276.8627   $276.86   $276.85   $276.90  
  Purchase #7 $16.64   12.174%   $18.6658   $18.67   $18.65   $18.70  
  7 purchase totals = $976.35       $1,067.8920   $1,067.89   $1,067.85   $1,067.90