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 $90.72   11.361%   $101.0267   $101.03   $101.05   $101.00  
  Purchase #2 $148.78   13.554%   $168.9456   $168.95   $168.95   $168.90  
  Purchase #3 $167.45   9.162%   $182.7918   $182.79   $182.80   $182.80  
  Purchase #4 $212.99   11.836%   $238.1995   $238.20   $238.20   $238.20  
  Purchase #5 $27.58   10.195%   $30.3918   $30.39   $30.40   $30.40  
  Purchase #6 $239.29   9.667%   $262.4222   $262.42   $262.40   $262.40  
  Purchase #7 $68.37   4.286%   $71.3003   $71.30   $71.30   $71.30  
  7 purchase totals = $955.18       $1,055.0779   $1,055.08   $1,055.10   $1,055.00