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 $77.46   13.609%   $88.0015   $88.00   $88.00   $88.00  
  Purchase #2 $143.67   10.744%   $159.1059   $159.11   $159.10   $159.10  
  Purchase #3 $26.26   4.131%   $27.3448   $27.34   $27.35   $27.30  
  Purchase #4 $170.57   12.697%   $192.2273   $192.23   $192.25   $192.20  
  Purchase #5 $162.85   7.457%   $174.9937   $174.99   $175.00   $175.00  
  Purchase #6 $70.37   6.582%   $75.0018   $75.00   $75.00   $75.00  
  Purchase #7 $237.51   6.258%   $252.3734   $252.37   $252.35   $252.40  
  7 purchase totals = $888.69       $969.0484   $969.04   $969.05   $969.00