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 $239.47   10.647%   $264.9664   $264.97   $264.95   $265.00  
  Purchase #2 $113.94   6.707%   $121.582   $121.58   $121.60   $121.60  
  Purchase #3 $244.40   3.379%   $252.6583   $252.66   $252.65   $252.70  
  Purchase #4 $152.95   7.669%   $164.6797   $164.68   $164.70   $164.70  
  Purchase #5 $213.31   4.334%   $222.5549   $222.55   $222.55   $222.60  
  Purchase #6 $154.65   6.809%   $165.1801   $165.18   $165.20   $165.20  
  Purchase #7 $6.87   6.871%   $7.342   $7.34   $7.35   $7.30  
  7 purchase totals = $1,125.59       $1,198.9634   $1,198.96   $1,199.00   $1,199.10