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 $95.41   12.821%   $107.6425   $107.64   $107.65   $107.60  
  Purchase #2 $235.49   13.163%   $266.4875   $266.49   $266.50   $266.50  
  Purchase #3 $232.57   6.570%   $247.8498   $247.85   $247.85   $247.80  
  Purchase #4 $133.64   5.315%   $140.743   $140.74   $140.75   $140.70  
  Purchase #5 $72.61   9.814%   $79.7359   $79.74   $79.75   $79.70  
  Purchase #6 $8.31   5.680%   $8.782   $8.78   $8.80   $8.80  
  Purchase #7 $136.88   5.721%   $144.7109   $144.71   $144.70   $144.70  
  7 purchase totals = $914.91       $995.9516   $995.95   $996.00   $995.80