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 $224.57   8.656%   $244.0088   $244.01   $244.00   $244.00  
  Purchase #2 $186.32   13.378%   $211.2459   $211.25   $211.25   $211.20  
  Purchase #3 $220.88   12.148%   $247.7125   $247.71   $247.70   $247.70  
  Purchase #4 $85.29   7.773%   $91.9196   $91.92   $91.90   $91.90  
  Purchase #5 $165.48   9.139%   $180.6032   $180.60   $180.60   $180.60  
  Purchase #6 $221.49   9.705%   $242.9856   $242.99   $243.00   $243.00  
  Purchase #7 $114.38   4.151%   $119.1279   $119.13   $119.15   $119.10  
  7 purchase totals = $1,218.41       $1,337.6035   $1,337.61   $1,337.60   $1,337.50