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 $217.58   13.667%   $247.3167   $247.32   $247.30   $247.30  
  Purchase #2 $181.62   12.157%   $203.6995   $203.70   $203.70   $203.70  
  Purchase #3 $229.98   3.156%   $237.2382   $237.24   $237.25   $237.20  
  Purchase #4 $88.38   10.491%   $97.6519   $97.65   $97.65   $97.70  
  Purchase #5 $137.45   3.128%   $141.7494   $141.75   $141.75   $141.70  
  Purchase #6 $134.72   5.764%   $142.4853   $142.49   $142.50   $142.50  
  Purchase #7 $37.56   13.166%   $42.5051   $42.51   $42.50   $42.50  
  7 purchase totals = $1,027.29       $1,112.6461   $1,112.66   $1,112.65   $1,112.60