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 $34.40   10.620%   $38.0533   $38.05   $38.05   $38.10  
  Purchase #2 $21.44   12.320%   $24.0814   $24.08   $24.10   $24.10  
  Purchase #3 $143.86   8.361%   $155.8881   $155.89   $155.90   $155.90  
  Purchase #4 $82.88   12.267%   $93.0469   $93.05   $93.05   $93.00  
  Purchase #5 $53.35   13.823%   $60.7246   $60.72   $60.70   $60.70  
  Purchase #6 $206.70   6.605%   $220.3525   $220.35   $220.35   $220.40  
  Purchase #7 $125.66   6.259%   $133.5251   $133.53   $133.55   $133.50  
  7 purchase totals = $668.29       $725.6719   $725.67   $725.70   $725.70