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 $58.84   8.619%   $63.9114   $63.91   $63.90   $63.90  
  Purchase #2 $30.95   12.586%   $34.8454   $34.85   $34.85   $34.80  
  Purchase #3 $241.51   9.632%   $264.7722   $264.77   $264.75   $264.80  
  Purchase #4 $166.53   10.705%   $184.357   $184.36   $184.35   $184.40  
  Purchase #5 $14.88   6.130%   $15.7921   $15.79   $15.80   $15.80  
  Purchase #6 $218.85   9.557%   $239.7655   $239.77   $239.75   $239.80  
  Purchase #7 $179.48   6.608%   $191.34   $191.34   $191.35   $191.30  
  7 purchase totals = $911.04       $994.7836   $994.79   $994.75   $994.80