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 $82.28   5.670%   $86.9453   $86.95   $86.95   $86.90  
  Purchase #2 $144.62   9.718%   $158.6742   $158.67   $158.65   $158.70  
  Purchase #3 $51.49   5.122%   $54.1273   $54.13   $54.15   $54.10  
  Purchase #4 $239.49   12.159%   $268.6096   $268.61   $268.60   $268.60  
  Purchase #5 $138.87   9.131%   $151.5502   $151.55   $151.55   $151.60  
  Purchase #6 $243.26   13.420%   $275.9055   $275.91   $275.90   $275.90  
  Purchase #7 $66.87   4.617%   $69.9574   $69.96   $69.95   $70.00  
  7 purchase totals = $966.88       $1,065.7695   $1,065.78   $1,065.75   $1,065.80