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 $19.54   13.112%   $22.1021   $22.10   $22.10   $22.10  
  Purchase #2 $21.43   7.521%   $23.0418   $23.04   $23.05   $23.00  
  Purchase #3 $140.25   11.232%   $156.0029   $156.00   $156.00   $156.00  
  Purchase #4 $75.71   10.204%   $83.4354   $83.44   $83.45   $83.40  
  Purchase #5 $148.66   7.626%   $159.9968   $160.00   $160.00   $160.00  
  Purchase #6 $80.39   6.635%   $85.7239   $85.72   $85.70   $85.70  
  Purchase #7 $179.66   10.846%   $199.1459   $199.15   $199.15   $199.10  
  7 purchase totals = $665.64       $729.4488   $729.45   $729.45   $729.30