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 $24.52   8.691%   $26.651   $26.65   $26.65   $26.70  
  Purchase #2 $53.64   13.754%   $61.0176   $61.02   $61.00   $61.00  
  Purchase #3 $95.25   7.193%   $102.1013   $102.10   $102.10   $102.10  
  Purchase #4 $58.58   5.729%   $61.936   $61.94   $61.95   $61.90  
  Purchase #5 $186.85   6.390%   $198.7897   $198.79   $198.80   $198.80  
  Purchase #6 $231.92   3.192%   $239.3229   $239.32   $239.30   $239.30  
  Purchase #7 $213.42   5.186%   $224.488   $224.49   $224.50   $224.50  
  7 purchase totals = $864.18       $914.3065   $914.31   $914.30   $914.30