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 $79.84   8.626%   $86.727   $86.73   $86.75   $86.70  
  Purchase #2 $14.36   8.780%   $15.6208   $15.62   $15.60   $15.60  
  Purchase #3 $216.48   4.867%   $227.0161   $227.02   $227.00   $227.00  
  Purchase #4 $201.92   3.465%   $208.9165   $208.92   $208.90   $208.90  
  Purchase #5 $87.45   12.168%   $98.0909   $98.09   $98.10   $98.10  
  Purchase #6 $249.54   5.764%   $263.9235   $263.92   $263.90   $263.90  
  Purchase #7 $128.83   5.499%   $135.9144   $135.91   $135.90   $135.90  
  7 purchase totals = $978.42       $1,036.2092   $1,036.21   $1,036.15   $1,036.10