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 $80.31   7.119%   $86.0273   $86.03   $86.05   $86.00  
  Purchase #2 $138.81   10.403%   $153.2504   $153.25   $153.25   $153.30  
  Purchase #3 $181.98   10.852%   $201.7285   $201.73   $201.75   $201.70  
  Purchase #4 $162.69   3.326%   $168.1011   $168.10   $168.10   $168.10  
  Purchase #5 $105.66   13.424%   $119.8438   $119.84   $119.85   $119.80  
  Purchase #6 $88.49   8.134%   $95.6878   $95.69   $95.70   $95.70  
  Purchase #7 $227.92   13.627%   $258.9787   $258.98   $259.00   $259.00  
  7 purchase totals = $985.86       $1,083.6176   $1,083.62   $1,083.70   $1,083.60