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 $174.54   4.552%   $182.4851   $182.49   $182.50   $182.50  
  Purchase #2 $248.79   11.368%   $277.0724   $277.07   $277.05   $277.10  
  Purchase #3 $29.56   13.584%   $33.5754   $33.58   $33.60   $33.60  
  Purchase #4 $101.80   7.836%   $109.777   $109.78   $109.80   $109.80  
  Purchase #5 $174.98   5.549%   $184.6896   $184.69   $184.70   $184.70  
  Purchase #6 $95.68   8.728%   $104.031   $104.03   $104.05   $104.00  
  Purchase #7 $223.34   4.150%   $232.6086   $232.61   $232.60   $232.60  
  7 purchase totals = $1,048.69       $1,124.2391   $1,124.25   $1,124.30   $1,124.30