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 $138.26   5.694%   $146.1325   $146.13   $146.15   $146.10  
  Purchase #2 $225.98   8.256%   $244.6369   $244.64   $244.65   $244.60  
  Purchase #3 $151.30   12.159%   $169.6966   $169.70   $169.70   $169.70  
  Purchase #4 $229.36   9.372%   $250.8556   $250.86   $250.85   $250.90  
  Purchase #5 $111.59   3.675%   $115.6909   $115.69   $115.70   $115.70  
  Purchase #6 $165.54   5.708%   $174.989   $174.99   $175.00   $175.00  
  Purchase #7 $247.94   7.756%   $267.1702   $267.17   $267.15   $267.20  
  7 purchase totals = $1,269.97       $1,369.1717   $1,369.18   $1,369.20   $1,369.20