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 $88.46   5.434%   $93.2669   $93.27   $93.25   $93.30  
  Purchase #2 $114.85   10.567%   $126.9862   $126.99   $127.00   $127.00  
  Purchase #3 $94.50   8.434%   $102.4701   $102.47   $102.45   $102.50  
  Purchase #4 $53.55   8.346%   $58.0193   $58.02   $58.00   $58.00  
  Purchase #5 $44.52   12.353%   $50.0196   $50.02   $50.00   $50.00  
  Purchase #6 $248.97   3.308%   $257.2059   $257.21   $257.20   $257.20  
  Purchase #7 $51.41   11.155%   $57.1448   $57.14   $57.15   $57.10  
  7 purchase totals = $696.26       $745.1128   $745.12   $745.05   $745.10