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 $61.80   8.436%   $67.0134   $67.01   $67.00   $67.00  
  Purchase #2 $7.46   6.626%   $7.9543   $7.95   $7.95   $8.00  
  Purchase #3 $112.78   10.294%   $124.3896   $124.39   $124.40   $124.40  
  Purchase #4 $99.63   4.246%   $103.8603   $103.86   $103.85   $103.90  
  Purchase #5 $223.63   4.548%   $233.8007   $233.80   $233.80   $233.80  
  Purchase #6 $163.49   6.721%   $174.4782   $174.48   $174.50   $174.50  
  Purchase #7 $191.63   10.846%   $212.4142   $212.41   $212.40   $212.40  
  7 purchase totals = $860.42       $923.9107   $923.90   $923.90   $924.00