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 $86.44   12.247%   $97.0263   $97.03   $97.05   $97.00  
  Purchase #2 $137.74   9.534%   $150.8721   $150.87   $150.85   $150.90  
  Purchase #3 $241.76   10.520%   $267.1932   $267.19   $267.20   $267.20  
  Purchase #4 $185.84   12.136%   $208.3935   $208.39   $208.40   $208.40  
  Purchase #5 $130.29   12.626%   $146.7404   $146.74   $146.75   $146.70  
  Purchase #6 $186.79   5.366%   $196.8132   $196.81   $196.80   $196.80  
  Purchase #7 $27.98   13.372%   $31.7215   $31.72   $31.70   $31.70  
  7 purchase totals = $996.84       $1,098.7602   $1,098.75   $1,098.75   $1,098.70