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 $44.94   7.615%   $48.3622   $48.36   $48.35   $48.40  
  Purchase #2 $70.93   5.696%   $74.9702   $74.97   $74.95   $75.00  
  Purchase #3 $198.81   5.392%   $209.5298   $209.53   $209.55   $209.50  
  Purchase #4 $180.67   9.270%   $197.4181   $197.42   $197.40   $197.40  
  Purchase #5 $134.78   7.531%   $144.9303   $144.93   $144.95   $144.90  
  Purchase #6 $167.92   10.167%   $184.9924   $184.99   $185.00   $185.00  
  Purchase #7 $149.36   12.563%   $168.1241   $168.12   $168.10   $168.10  
  7 purchase totals = $947.41       $1,028.3271   $1,028.32   $1,028.30   $1,028.30