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 $78.99   8.175%   $85.4474   $85.45   $85.45   $85.40  
  Purchase #2 $246.80   6.179%   $262.0498   $262.05   $262.05   $262.00  
  Purchase #3 $191.85   8.402%   $207.9692   $207.97   $207.95   $208.00  
  Purchase #4 $157.91   9.705%   $173.2352   $173.24   $173.25   $173.20  
  Purchase #5 $165.26   5.660%   $174.6137   $174.61   $174.60   $174.60  
  Purchase #6 $181.30   7.517%   $194.9283   $194.93   $194.95   $194.90  
  Purchase #7 $186.83   9.721%   $204.9917   $204.99   $205.00   $205.00  
  7 purchase totals = $1,208.94       $1,303.2353   $1,303.24   $1,303.25   $1,303.10