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 $52.67   8.516%   $57.1554   $57.16   $57.15   $57.20  
  Purchase #2 $142.74   13.463%   $161.9571   $161.96   $161.95   $162.00  
  Purchase #3 $101.32   13.189%   $114.6831   $114.68   $114.70   $114.70  
  Purchase #4 $209.43   12.695%   $236.0171   $236.02   $236.00   $236.00  
  Purchase #5 $231.70   7.231%   $248.4542   $248.45   $248.45   $248.50  
  Purchase #6 $234.58   8.737%   $255.0753   $255.08   $255.10   $255.10  
  Purchase #7 $23.46   3.698%   $24.3276   $24.33   $24.35   $24.30  
  7 purchase totals = $995.90       $1,097.6698   $1,097.68   $1,097.70   $1,097.80