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 $46.89   4.404%   $48.955   $48.96   $48.95   $49.00  
  Purchase #2 $14.82   6.839%   $15.8335   $15.83   $15.85   $15.80  
  Purchase #3 $58.25   13.771%   $66.2716   $66.27   $66.25   $66.30  
  Purchase #4 $219.99   5.828%   $232.811   $232.81   $232.80   $232.80  
  Purchase #5 $211.71   3.188%   $218.4593   $218.46   $218.45   $218.50  
  Purchase #6 $194.99   5.492%   $205.6989   $205.70   $205.70   $205.70  
  Purchase #7 $128.88   8.648%   $140.0255   $140.03   $140.05   $140.00  
  7 purchase totals = $875.53       $928.0548   $928.06   $928.05   $928.10