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 $162.46   8.593%   $176.4202   $176.42   $176.40   $176.40  
  Purchase #2 $241.53   13.395%   $273.8829   $273.88   $273.90   $273.90  
  Purchase #3 $54.37   12.479%   $61.1548   $61.15   $61.15   $61.20  
  Purchase #4 $121.43   9.596%   $133.0824   $133.08   $133.10   $133.10  
  Purchase #5 $175.63   12.848%   $198.1949   $198.19   $198.20   $198.20  
  Purchase #6 $91.95   4.152%   $95.7678   $95.77   $95.75   $95.80  
  Purchase #7 $103.80   8.587%   $112.7133   $112.71   $112.70   $112.70  
  7 purchase totals = $951.17       $1,051.2163   $1,051.20   $1,051.20   $1,051.30