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 $107.99   3.580%   $111.856   $111.86   $111.85   $111.90  
  Purchase #2 $93.55   4.339%   $97.6091   $97.61   $97.60   $97.60  
  Purchase #3 $23.51   8.615%   $25.5354   $25.54   $25.55   $25.50  
  Purchase #4 $215.39   5.609%   $227.4712   $227.47   $227.45   $227.50  
  Purchase #5 $62.53   5.454%   $65.9404   $65.94   $65.95   $65.90  
  Purchase #6 $208.34   11.839%   $233.0054   $233.01   $233.00   $233.00  
  Purchase #7 $214.39   9.187%   $234.086   $234.09   $234.10   $234.10  
  7 purchase totals = $925.70       $995.5035   $995.52   $995.50   $995.50