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 $49.33   10.702%   $54.6093   $54.61   $54.60   $54.60  
  Purchase #2 $88.94   3.736%   $92.2628   $92.26   $92.25   $92.30  
  Purchase #3 $79.55   3.535%   $82.3621   $82.36   $82.35   $82.40  
  Purchase #4 $190.31   8.678%   $206.8251   $206.83   $206.85   $206.80  
  Purchase #5 $185.76   11.776%   $207.6351   $207.64   $207.65   $207.60  
  Purchase #6 $31.96   11.186%   $35.535   $35.54   $35.55   $35.50  
  Purchase #7 $246.29   4.845%   $258.2228   $258.22   $258.20   $258.20  
  7 purchase totals = $872.14       $937.4522   $937.46   $937.45   $937.40