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 $165.58   10.561%   $183.0669   $183.07   $183.05   $183.10  
  Purchase #2 $156.99   11.358%   $174.8209   $174.82   $174.80   $174.80  
  Purchase #3 $111.72   4.557%   $116.8111   $116.81   $116.80   $116.80  
  Purchase #4 $207.52   6.734%   $221.4944   $221.49   $221.50   $221.50  
  Purchase #5 $241.75   9.715%   $265.236   $265.24   $265.25   $265.20  
  Purchase #6 $163.68   7.369%   $175.7416   $175.74   $175.75   $175.70  
  Purchase #7 $187.82   5.783%   $198.6816   $198.68   $198.70   $198.70  
  7 purchase totals = $1,235.06       $1,335.8525   $1,335.85   $1,335.85   $1,335.80