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 $87.68   11.724%   $97.9596   $97.96   $97.95   $98.00  
  Purchase #2 $201.78   12.632%   $227.2688   $227.27   $227.25   $227.30  
  Purchase #3 $101.89   4.540%   $106.5158   $106.52   $106.50   $106.50  
  Purchase #4 $31.60   11.577%   $35.2583   $35.26   $35.25   $35.30  
  Purchase #5 $114.44   4.846%   $119.9858   $119.99   $120.00   $120.00  
  Purchase #6 $30.51   6.508%   $32.4956   $32.50   $32.50   $32.50  
  Purchase #7 $40.43   12.332%   $45.4158   $45.42   $45.40   $45.40  
  7 purchase totals = $608.33       $664.8997   $664.92   $664.85   $665.00