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 $100.96   13.256%   $114.3433   $114.34   $114.35   $114.30  
  Purchase #2 $54.86   10.278%   $60.4985   $60.50   $60.50   $60.50  
  Purchase #3 $98.52   4.792%   $103.2411   $103.24   $103.25   $103.20  
  Purchase #4 $56.95   8.229%   $61.6364   $61.64   $61.65   $61.60  
  Purchase #5 $213.96   7.511%   $230.0305   $230.03   $230.05   $230.00  
  Purchase #6 $213.74   6.874%   $228.4325   $228.43   $228.45   $228.40  
  Purchase #7 $223.32   5.813%   $236.3016   $236.30   $236.30   $236.30  
  7 purchase totals = $962.31       $1,034.4839   $1,034.48   $1,034.55   $1,034.30