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 $93.58   8.744%   $101.7626   $101.76   $101.75   $101.80  
  Purchase #2 $48.65   11.598%   $54.2924   $54.29   $54.30   $54.30  
  Purchase #3 $38.92   8.478%   $42.2196   $42.22   $42.20   $42.20  
  Purchase #4 $60.37   3.862%   $62.7015   $62.70   $62.70   $62.70  
  Purchase #5 $53.49   6.439%   $56.9342   $56.93   $56.95   $56.90  
  Purchase #6 $204.95   3.405%   $211.9285   $211.93   $211.95   $211.90  
  Purchase #7 $21.71   3.479%   $22.4653   $22.47   $22.45   $22.50  
  7 purchase totals = $521.67       $552.3041   $552.30   $552.30   $552.30