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 $232.43   12.154%   $260.6795   $260.68   $260.70   $260.70  
  Purchase #2 $47.25   6.569%   $50.3539   $50.35   $50.35   $50.40  
  Purchase #3 $250.52   3.545%   $259.4009   $259.40   $259.40   $259.40  
  Purchase #4 $127.30   4.161%   $132.597   $132.60   $132.60   $132.60  
  Purchase #5 $152.48   13.786%   $173.5009   $173.50   $173.50   $173.50  
  Purchase #6 $96.79   3.490%   $100.168   $100.17   $100.15   $100.20  
  Purchase #7 $44.45   13.186%   $50.3112   $50.31   $50.30   $50.30  
  7 purchase totals = $951.22       $1,027.0114   $1,027.01   $1,027.00   $1,027.10