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 $80.59   6.655%   $85.9533   $85.95   $85.95   $86.00  
  Purchase #2 $179.41   13.143%   $202.9899   $202.99   $203.00   $203.00  
  Purchase #3 $43.74   13.699%   $49.7319   $49.73   $49.75   $49.70  
  Purchase #4 $109.91   6.532%   $117.0893   $117.09   $117.10   $117.10  
  Purchase #5 $66.96   7.841%   $72.2103   $72.21   $72.20   $72.20  
  Purchase #6 $16.53   11.788%   $18.4786   $18.48   $18.50   $18.50  
  Purchase #7 $69.53   13.666%   $79.032   $79.03   $79.05   $79.00  
  7 purchase totals = $566.67       $625.4853   $625.48   $625.55   $625.50