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 $197.76   6.836%   $211.2789   $211.28   $211.30   $211.30  
  Purchase #2 $133.55   4.723%   $139.8576   $139.86   $139.85   $139.90  
  Purchase #3 $153.66   12.418%   $172.7415   $172.74   $172.75   $172.70  
  Purchase #4 $42.55   11.564%   $47.4705   $47.47   $47.45   $47.50  
  Purchase #5 $202.39   11.374%   $225.4098   $225.41   $225.40   $225.40  
  Purchase #6 $129.41   8.684%   $140.648   $140.65   $140.65   $140.60  
  Purchase #7 $246.63   7.851%   $265.9929   $265.99   $266.00   $266.00  
  7 purchase totals = $1,105.95       $1,203.3992   $1,203.40   $1,203.40   $1,203.40