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 $239.46   8.771%   $260.463   $260.46   $260.45   $260.50  
  Purchase #2 $104.74   8.395%   $113.5329   $113.53   $113.55   $113.50  
  Purchase #3 $165.39   7.218%   $177.3279   $177.33   $177.35   $177.30  
  Purchase #4 $119.89   12.608%   $135.0057   $135.01   $135.00   $135.00  
  Purchase #5 $20.53   12.573%   $23.1112   $23.11   $23.10   $23.10  
  Purchase #6 $237.38   12.474%   $266.9908   $266.99   $267.00   $267.00  
  Purchase #7 $96.97   3.209%   $100.0818   $100.08   $100.10   $100.10  
  7 purchase totals = $984.36       $1,076.5133   $1,076.51   $1,076.55   $1,076.50