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 $87.77   6.691%   $93.6427   $93.64   $93.65   $93.60  
  Purchase #2 $45.92   8.602%   $49.87   $49.87   $49.85   $49.90  
  Purchase #3 $8.45   7.273%   $9.0646   $9.06   $9.05   $9.10  
  Purchase #4 $64.70   5.787%   $68.4442   $68.44   $68.45   $68.40  
  Purchase #5 $15.47   4.735%   $16.2025   $16.20   $16.20   $16.20  
  Purchase #6 $47.61   12.522%   $53.5717   $53.57   $53.55   $53.60  
  Purchase #7 $212.41   12.824%   $239.6495   $239.65   $239.65   $239.60  
  7 purchase totals = $482.33       $530.4452   $530.43   $530.40   $530.40