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 $201.73   3.358%   $208.5041   $208.50   $208.50   $208.50  
  Purchase #2 $190.54   11.299%   $212.0691   $212.07   $212.05   $212.10  
  Purchase #3 $34.46   10.734%   $38.1589   $38.16   $38.15   $38.20  
  Purchase #4 $194.57   6.658%   $207.5245   $207.52   $207.50   $207.50  
  Purchase #5 $202.59   10.803%   $224.4758   $224.48   $224.50   $224.50  
  Purchase #6 $26.52   10.157%   $29.2136   $29.21   $29.20   $29.20  
  Purchase #7 $116.59   12.531%   $131.1999   $131.20   $131.20   $131.20  
  7 purchase totals = $967.00       $1,051.1459   $1,051.14   $1,051.10   $1,051.20