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 $44.76   12.405%   $50.3125   $50.31   $50.30   $50.30  
  Purchase #2 $207.83   5.313%   $218.872   $218.87   $218.85   $218.90  
  Purchase #3 $66.62   4.772%   $69.7991   $69.80   $69.80   $69.80  
  Purchase #4 $177.61   11.671%   $198.3389   $198.34   $198.35   $198.30  
  Purchase #5 $212.61   6.809%   $227.0866   $227.09   $227.10   $227.10  
  Purchase #6 $68.90   5.256%   $72.5214   $72.52   $72.50   $72.50  
  Purchase #7 $34.31   11.154%   $38.1369   $38.14   $38.15   $38.10  
  7 purchase totals = $812.64       $875.0674   $875.07   $875.05   $875.00