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 $68.27   7.859%   $73.6353   $73.64   $73.65   $73.60  
  Purchase #2 $169.42   4.360%   $176.8067   $176.81   $176.80   $176.80  
  Purchase #3 $142.46   6.341%   $151.4934   $151.49   $151.50   $151.50  
  Purchase #4 $163.68   6.601%   $174.4845   $174.48   $174.50   $174.50  
  Purchase #5 $33.64   8.419%   $36.4722   $36.47   $36.45   $36.50  
  Purchase #6 $149.53   11.121%   $166.1592   $166.16   $166.15   $166.20  
  Purchase #7 $181.50   4.683%   $189.9996   $190.00   $190.00   $190.00  
  7 purchase totals = $908.50       $969.0509   $969.05   $969.05   $969.10