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 $157.68   6.289%   $167.5965   $167.60   $167.60   $167.60  
  Purchase #2 $14.75   7.479%   $15.8532   $15.85   $15.85   $15.90  
  Purchase #3 $162.99   8.869%   $177.4456   $177.45   $177.45   $177.40  
  Purchase #4 $56.68   6.856%   $60.566   $60.57   $60.55   $60.60  
  Purchase #5 $66.59   6.486%   $70.909   $70.91   $70.90   $70.90  
  Purchase #6 $244.60   9.379%   $267.541   $267.54   $267.55   $267.50  
  Purchase #7 $36.25   7.438%   $38.9463   $38.95   $38.95   $38.90  
  7 purchase totals = $739.54       $798.8576   $798.87   $798.85   $798.80