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 $113.55   11.761%   $126.9046   $126.90   $126.90   $126.90  
  Purchase #2 $213.68   12.204%   $239.7575   $239.76   $239.75   $239.80  
  Purchase #3 $55.39   11.212%   $61.6003   $61.60   $61.60   $61.60  
  Purchase #4 $194.55   6.685%   $207.5557   $207.56   $207.55   $207.60  
  Purchase #5 $14.65   9.285%   $16.0103   $16.01   $16.00   $16.00  
  Purchase #6 $70.34   5.753%   $74.3867   $74.39   $74.40   $74.40  
  Purchase #7 $74.33   11.246%   $82.6892   $82.69   $82.70   $82.70  
  7 purchase totals = $736.49       $808.9043   $808.91   $808.90   $809.00