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 $108.61   5.289%   $114.3544   $114.35   $114.35   $114.40  
  Purchase #2 $88.92   7.178%   $95.3027   $95.30   $95.30   $95.30  
  Purchase #3 $156.39   13.806%   $177.9812   $177.98   $178.00   $178.00  
  Purchase #4 $154.72   11.304%   $172.2095   $172.21   $172.20   $172.20  
  Purchase #5 $158.47   5.694%   $167.4933   $167.49   $167.50   $167.50  
  Purchase #6 $246.93   12.117%   $276.8505   $276.85   $276.85   $276.90  
  Purchase #7 $65.68   3.209%   $67.7877   $67.79   $67.80   $67.80  
  7 purchase totals = $979.72       $1,071.9793   $1,071.97   $1,072.00   $1,072.10