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 $217.36   5.721%   $229.7952   $229.80   $229.80   $229.80  
  Purchase #2 $71.68   9.436%   $78.4437   $78.44   $78.45   $78.40  
  Purchase #3 $248.88   7.645%   $267.9069   $267.91   $267.90   $267.90  
  Purchase #4 $77.95   10.590%   $86.2049   $86.20   $86.20   $86.20  
  Purchase #5 $23.95   6.211%   $25.4375   $25.44   $25.45   $25.40  
  Purchase #6 $174.38   5.691%   $184.304   $184.30   $184.30   $184.30  
  Purchase #7 $117.94   9.156%   $128.7386   $128.74   $128.75   $128.70  
  7 purchase totals = $932.14       $1,000.8308   $1,000.83   $1,000.85   $1,000.70