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 $91.78   5.478%   $96.8077   $96.81   $96.80   $96.80  
  Purchase #2 $239.68   10.546%   $264.9567   $264.96   $264.95   $265.00  
  Purchase #3 $142.28   3.723%   $147.5771   $147.58   $147.60   $147.60  
  Purchase #4 $222.27   4.454%   $232.1699   $232.17   $232.15   $232.20  
  Purchase #5 $217.42   10.377%   $239.9817   $239.98   $240.00   $240.00  
  Purchase #6 $171.64   11.863%   $192.0017   $192.00   $192.00   $192.00  
  Purchase #7 $110.62   8.120%   $119.6023   $119.60   $119.60   $119.60  
  7 purchase totals = $1,195.69       $1,293.0971   $1,293.10   $1,293.10   $1,293.20