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 $206.72   8.622%   $224.5434   $224.54   $224.55   $224.50  
  Purchase #2 $42.34   6.330%   $45.0201   $45.02   $45.00   $45.00  
  Purchase #3 $119.93   4.493%   $125.3185   $125.32   $125.30   $125.30  
  Purchase #4 $153.77   11.220%   $171.023   $171.02   $171.00   $171.00  
  Purchase #5 $41.71   7.573%   $44.8687   $44.87   $44.85   $44.90  
  Purchase #6 $203.75   12.248%   $228.7053   $228.71   $228.70   $228.70  
  Purchase #7 $108.61   5.657%   $114.7541   $114.75   $114.75   $114.80  
  7 purchase totals = $876.83       $954.2331   $954.23   $954.15   $954.20