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 $24.51   9.510%   $26.8409   $26.84   $26.85   $26.80  
  Purchase #2 $107.26   13.761%   $122.02   $122.02   $122.00   $122.00  
  Purchase #3 $238.71   11.757%   $266.7751   $266.78   $266.80   $266.80  
  Purchase #4 $211.57   8.505%   $229.564   $229.56   $229.55   $229.60  
  Purchase #5 $167.28   6.648%   $178.4008   $178.40   $178.40   $178.40  
  Purchase #6 $117.91   5.806%   $124.7559   $124.76   $124.75   $124.80  
  Purchase #7 $12.80   6.801%   $13.6705   $13.67   $13.65   $13.70  
  7 purchase totals = $880.04       $962.0272   $962.03   $962.00   $962.10