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 $246.54   11.218%   $274.1969   $274.20   $274.20   $274.20  
  Purchase #2 $107.31   6.157%   $113.9171   $113.92   $113.90   $113.90  
  Purchase #3 $196.79   5.772%   $208.1487   $208.15   $208.15   $208.10  
  Purchase #4 $58.99   3.571%   $61.0965   $61.10   $61.10   $61.10  
  Purchase #5 $40.35   9.544%   $44.201   $44.20   $44.20   $44.20  
  Purchase #6 $177.84   5.545%   $187.7012   $187.70   $187.70   $187.70  
  Purchase #7 $83.46   8.140%   $90.2536   $90.25   $90.25   $90.30  
  7 purchase totals = $911.28       $979.5150   $979.52   $979.50   $979.50