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 $66.37   10.322%   $73.2207   $73.22   $73.20   $73.20  
  Purchase #2 $127.50   12.135%   $142.9721   $142.97   $142.95   $143.00  
  Purchase #3 $104.61   3.708%   $108.4889   $108.49   $108.50   $108.50  
  Purchase #4 $243.85   10.263%   $268.8763   $268.88   $268.90   $268.90  
  Purchase #5 $173.36   12.800%   $195.5501   $195.55   $195.55   $195.60  
  Purchase #6 $164.86   10.390%   $181.989   $181.99   $182.00   $182.00  
  Purchase #7 $181.99   12.677%   $205.0609   $205.06   $205.05   $205.10  
  7 purchase totals = $1,062.54       $1,176.1580   $1,176.16   $1,176.15   $1,176.30