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 $242.57   8.113%   $262.2497   $262.25   $262.25   $262.20  
  Purchase #2 $141.67   7.543%   $152.3562   $152.36   $152.35   $152.40  
  Purchase #3 $5.45   11.537%   $6.0788   $6.08   $6.10   $6.10  
  Purchase #4 $68.95   7.391%   $74.0461   $74.05   $74.05   $74.00  
  Purchase #5 $32.29   4.642%   $33.7889   $33.79   $33.80   $33.80  
  Purchase #6 $12.44   8.141%   $13.4527   $13.45   $13.45   $13.50  
  Purchase #7 $192.80   8.581%   $209.3442   $209.34   $209.35   $209.30  
  7 purchase totals = $696.17       $751.3166   $751.32   $751.35   $751.30