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 $202.40   11.659%   $225.9978   $226.00   $226.00   $226.00  
  Purchase #2 $86.88   11.452%   $96.8295   $96.83   $96.85   $96.80  
  Purchase #3 $198.83   6.179%   $211.1157   $211.12   $211.10   $211.10  
  Purchase #4 $73.57   3.761%   $76.337   $76.34   $76.35   $76.30  
  Purchase #5 $169.34   5.474%   $178.6097   $178.61   $178.60   $178.60  
  Purchase #6 $159.99   3.469%   $165.5401   $165.54   $165.55   $165.50  
  Purchase #7 $34.39   12.795%   $38.7902   $38.79   $38.80   $38.80  
  7 purchase totals = $925.40       $993.2200   $993.23   $993.25   $993.10