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 $49.48   11.848%   $55.3424   $55.34   $55.35   $55.30  
  Purchase #2 $215.53   8.364%   $233.5569   $233.56   $233.55   $233.60  
  Purchase #3 $72.97   8.781%   $79.3775   $79.38   $79.40   $79.40  
  Purchase #4 $182.41   5.488%   $192.4207   $192.42   $192.40   $192.40  
  Purchase #5 $83.57   13.758%   $95.0676   $95.07   $95.05   $95.10  
  Purchase #6 $175.97   8.480%   $190.8923   $190.89   $190.90   $190.90  
  Purchase #7 $189.77   6.676%   $202.439   $202.44   $202.45   $202.40  
  7 purchase totals = $969.70       $1,049.0964   $1,049.10   $1,049.10   $1,049.10