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 $23.41   5.579%   $24.716   $24.72   $24.70   $24.70  
  Purchase #2 $57.46   9.639%   $62.9986   $63.00   $63.00   $63.00  
  Purchase #3 $7.99   5.185%   $8.4043   $8.40   $8.40   $8.40  
  Purchase #4 $45.27   8.233%   $48.9971   $49.00   $49.00   $49.00  
  Purchase #5 $150.85   6.688%   $160.9388   $160.94   $160.95   $160.90  
  Purchase #6 $27.55   8.747%   $29.9598   $29.96   $29.95   $30.00  
  Purchase #7 $30.76   6.779%   $32.8452   $32.85   $32.85   $32.80  
  7 purchase totals = $343.29       $368.8598   $368.87   $368.85   $368.80