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 $141.43   3.603%   $146.5257   $146.53   $146.55   $146.50  
  Purchase #2 $125.57   13.363%   $142.3499   $142.35   $142.35   $142.30  
  Purchase #3 $169.35   6.557%   $180.4543   $180.45   $180.45   $180.50  
  Purchase #4 $169.56   8.561%   $184.076   $184.08   $184.10   $184.10  
  Purchase #5 $114.67   9.233%   $125.2575   $125.26   $125.25   $125.30  
  Purchase #6 $146.31   5.804%   $154.8018   $154.80   $154.80   $154.80  
  Purchase #7 $86.58   4.553%   $90.522   $90.52   $90.50   $90.50  
  7 purchase totals = $953.47       $1,023.9872   $1,023.99   $1,024.00   $1,024.00