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 $217.36   13.564%   $246.8427   $246.84   $246.85   $246.80  
  Purchase #2 $116.98   4.644%   $122.4126   $122.41   $122.40   $122.40  
  Purchase #3 $165.51   7.122%   $177.2976   $177.30   $177.30   $177.30  
  Purchase #4 $7.44   3.824%   $7.7245   $7.72   $7.70   $7.70  
  Purchase #5 $139.94   9.406%   $153.1028   $153.10   $153.10   $153.10  
  Purchase #6 $104.61   6.349%   $111.2517   $111.25   $111.25   $111.30  
  Purchase #7 $103.61   4.540%   $108.3139   $108.31   $108.30   $108.30  
  7 purchase totals = $855.45       $926.9458   $926.93   $926.90   $926.90