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 $208.71   11.261%   $232.2128   $232.21   $232.20   $232.20  
  Purchase #2 $60.30   5.504%   $63.6189   $63.62   $63.60   $63.60  
  Purchase #3 $27.74   8.320%   $30.048   $30.05   $30.05   $30.00  
  Purchase #4 $97.26   7.160%   $104.2238   $104.22   $104.20   $104.20  
  Purchase #5 $47.34   11.428%   $52.75   $52.75   $52.75   $52.80  
  Purchase #6 $237.42   11.521%   $264.7732   $264.77   $264.75   $264.80  
  Purchase #7 $176.60   13.776%   $200.9284   $200.93   $200.95   $200.90  
  7 purchase totals = $855.37       $948.5551   $948.55   $948.50   $948.50