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 $86.78   7.866%   $93.6061   $93.61   $93.60   $93.60  
  Purchase #2 $188.85   10.372%   $208.4375   $208.44   $208.45   $208.40  
  Purchase #3 $12.78   11.832%   $14.2921   $14.29   $14.30   $14.30  
  Purchase #4 $91.39   5.836%   $96.7235   $96.72   $96.70   $96.70  
  Purchase #5 $179.75   8.767%   $195.5087   $195.51   $195.50   $195.50  
  Purchase #6 $237.86   13.825%   $270.7441   $270.74   $270.75   $270.70  
  Purchase #7 $147.71   12.475%   $166.1368   $166.14   $166.15   $166.10  
  7 purchase totals = $945.12       $1,045.4488   $1,045.45   $1,045.45   $1,045.30