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 $248.25   7.649%   $267.2386   $267.24   $267.25   $267.20  
  Purchase #2 $55.38   12.187%   $62.1292   $62.13   $62.15   $62.10  
  Purchase #3 $185.32   8.471%   $201.0185   $201.02   $201.00   $201.00  
  Purchase #4 $10.87   6.857%   $11.6154   $11.62   $11.60   $11.60  
  Purchase #5 $150.83   6.735%   $160.9884   $160.99   $161.00   $161.00  
  Purchase #6 $231.79   3.552%   $240.0232   $240.02   $240.00   $240.00  
  Purchase #7 $153.75   11.662%   $171.6803   $171.68   $171.70   $171.70  
  7 purchase totals = $1,036.19       $1,114.6936   $1,114.70   $1,114.70   $1,114.60