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 $74.86   6.188%   $79.4923   $79.49   $79.50   $79.50  
  Purchase #2 $183.67   10.818%   $203.5394   $203.54   $203.55   $203.50  
  Purchase #3 $23.67   7.202%   $25.3747   $25.37   $25.35   $25.40  
  Purchase #4 $191.62   8.651%   $208.197   $208.20   $208.20   $208.20  
  Purchase #5 $152.44   6.574%   $162.4614   $162.46   $162.45   $162.50  
  Purchase #6 $157.41   5.552%   $166.1494   $166.15   $166.15   $166.10  
  Purchase #7 $167.54   8.273%   $181.4006   $181.40   $181.40   $181.40  
  7 purchase totals = $951.21       $1,026.6148   $1,026.61   $1,026.60   $1,026.60