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 $247.65   7.745%   $266.8305   $266.83   $266.85   $266.80  
  Purchase #2 $19.26   5.699%   $20.3576   $20.36   $20.35   $20.40  
  Purchase #3 $60.62   6.602%   $64.6221   $64.62   $64.60   $64.60  
  Purchase #4 $124.35   8.106%   $134.4298   $134.43   $134.45   $134.40  
  Purchase #5 $208.57   8.152%   $225.5726   $225.57   $225.55   $225.60  
  Purchase #6 $184.59   13.292%   $209.1257   $209.13   $209.15   $209.10  
  Purchase #7 $70.46   5.477%   $74.3191   $74.32   $74.30   $74.30  
  7 purchase totals = $915.50       $995.2574   $995.26   $995.25   $995.20