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 $202.76   9.307%   $221.6309   $221.63   $221.65   $221.60  
  Purchase #2 $224.86   3.455%   $232.6289   $232.63   $232.65   $232.60  
  Purchase #3 $217.69   8.282%   $235.7191   $235.72   $235.70   $235.70  
  Purchase #4 $155.93   12.533%   $175.4727   $175.47   $175.45   $175.50  
  Purchase #5 $88.47   7.582%   $95.1778   $95.18   $95.20   $95.20  
  Purchase #6 $165.95   11.717%   $185.3944   $185.39   $185.40   $185.40  
  Purchase #7 $147.55   9.728%   $161.9037   $161.90   $161.90   $161.90  
  7 purchase totals = $1,203.21       $1,307.9275   $1,307.92   $1,307.95   $1,307.90