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 $88.26   6.274%   $93.7974   $93.80   $93.80   $93.80  
  Purchase #2 $47.84   3.858%   $49.6857   $49.69   $49.70   $49.70  
  Purchase #3 $23.49   10.161%   $25.8768   $25.88   $25.90   $25.90  
  Purchase #4 $138.81   12.612%   $156.3167   $156.32   $156.30   $156.30  
  Purchase #5 $232.53   11.391%   $259.0175   $259.02   $259.00   $259.00  
  Purchase #6 $126.35   13.834%   $143.8293   $143.83   $143.85   $143.80  
  Purchase #7 $224.69   11.139%   $249.7182   $249.72   $249.70   $249.70  
  7 purchase totals = $881.97       $978.2416   $978.26   $978.25   $978.20