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 $228.29   7.626%   $245.6994   $245.70   $245.70   $245.70  
  Purchase #2 $91.85   10.679%   $101.6587   $101.66   $101.65   $101.70  
  Purchase #3 $97.41   12.583%   $109.6671   $109.67   $109.65   $109.70  
  Purchase #4 $49.74   3.344%   $51.4033   $51.40   $51.40   $51.40  
  Purchase #5 $28.41   8.825%   $30.9172   $30.92   $30.90   $30.90  
  Purchase #6 $51.96   8.499%   $56.3761   $56.38   $56.40   $56.40  
  Purchase #7 $229.56   7.636%   $247.0892   $247.09   $247.10   $247.10  
  7 purchase totals = $777.22       $842.8110   $842.82   $842.80   $842.90