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 $97.46   12.395%   $109.5402   $109.54   $109.55   $109.50  
  Purchase #2 $201.55   4.484%   $210.5875   $210.59   $210.60   $210.60  
  Purchase #3 $22.42   5.497%   $23.6524   $23.65   $23.65   $23.70  
  Purchase #4 $9.28   9.461%   $10.158   $10.16   $10.15   $10.20  
  Purchase #5 $119.49   13.692%   $135.8506   $135.85   $135.85   $135.90  
  Purchase #6 $245.70   13.831%   $279.6828   $279.68   $279.70   $279.70  
  Purchase #7 $237.92   4.476%   $248.5693   $248.57   $248.55   $248.60  
  7 purchase totals = $933.82       $1,018.0408   $1,018.04   $1,018.05   $1,018.20