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 $195.46   11.539%   $218.0141   $218.01   $218.00   $218.00  
  Purchase #2 $94.97   6.701%   $101.3339   $101.33   $101.35   $101.30  
  Purchase #3 $77.41   11.329%   $86.1798   $86.18   $86.20   $86.20  
  Purchase #4 $225.66   10.475%   $249.2979   $249.30   $249.30   $249.30  
  Purchase #5 $163.40   10.592%   $180.7073   $180.71   $180.70   $180.70  
  Purchase #6 $89.68   12.543%   $100.9286   $100.93   $100.95   $100.90  
  Purchase #7 $120.42   3.455%   $124.5805   $124.58   $124.60   $124.60  
  7 purchase totals = $967.00       $1,061.0421   $1,061.04   $1,061.10   $1,061.00