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 $153.65   10.461%   $169.7233   $169.72   $169.70   $169.70  
  Purchase #2 $169.46   9.874%   $186.1925   $186.19   $186.20   $186.20  
  Purchase #3 $215.45   3.864%   $223.775   $223.78   $223.80   $223.80  
  Purchase #4 $205.46   12.698%   $231.5493   $231.55   $231.55   $231.50  
  Purchase #5 $74.67   3.666%   $77.4074   $77.41   $77.40   $77.40  
  Purchase #6 $117.37   5.491%   $123.8148   $123.81   $123.80   $123.80  
  Purchase #7 $58.73   9.734%   $64.4468   $64.45   $64.45   $64.40  
  7 purchase totals = $994.79       $1,076.9091   $1,076.91   $1,076.90   $1,076.80