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 $245.69   5.431%   $259.0334   $259.03   $259.05   $259.00  
  Purchase #2 $105.62   4.220%   $110.0772   $110.08   $110.10   $110.10  
  Purchase #3 $181.90   13.784%   $206.9731   $206.97   $206.95   $207.00  
  Purchase #4 $47.94   12.534%   $53.9488   $53.95   $53.95   $53.90  
  Purchase #5 $215.28   7.728%   $231.9168   $231.92   $231.90   $231.90  
  Purchase #6 $56.54   10.313%   $62.371   $62.37   $62.35   $62.40  
  Purchase #7 $46.95   5.869%   $49.7055   $49.71   $49.70   $49.70  
  7 purchase totals = $899.92       $974.0258   $974.03   $974.00   $974.00