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 $14.80   4.843%   $15.5168   $15.52   $15.50   $15.50  
  Purchase #2 $64.63   8.314%   $70.0033   $70.00   $70.00   $70.00  
  Purchase #3 $52.97   6.755%   $56.5481   $56.55   $56.55   $56.50  
  Purchase #4 $154.30   8.832%   $167.9278   $167.93   $167.95   $167.90  
  Purchase #5 $164.76   11.475%   $183.6662   $183.67   $183.65   $183.70  
  Purchase #6 $241.31   8.544%   $261.9275   $261.93   $261.95   $261.90  
  Purchase #7 $238.98   5.819%   $252.8862   $252.89   $252.90   $252.90  
  7 purchase totals = $931.75       $1,008.4759   $1,008.49   $1,008.50   $1,008.40