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 $57.57   7.691%   $61.9977   $62.00   $62.00   $62.00  
  Purchase #2 $157.82   12.617%   $177.7321   $177.73   $177.75   $177.70  
  Purchase #3 $64.87   13.620%   $73.7053   $73.71   $73.70   $73.70  
  Purchase #4 $11.79   12.554%   $13.2701   $13.27   $13.25   $13.30  
  Purchase #5 $226.56   11.184%   $251.8985   $251.90   $251.90   $251.90  
  Purchase #6 $112.46   10.283%   $124.0243   $124.02   $124.00   $124.00  
  Purchase #7 $191.26   3.592%   $198.1301   $198.13   $198.15   $198.10  
  7 purchase totals = $822.33       $900.7581   $900.76   $900.75   $900.70