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 $160.46   7.331%   $172.2233   $172.22   $172.20   $172.20  
  Purchase #2 $236.52   11.475%   $263.6607   $263.66   $263.65   $263.70  
  Purchase #3 $104.69   9.112%   $114.2294   $114.23   $114.25   $114.20  
  Purchase #4 $228.49   8.770%   $248.5286   $248.53   $248.55   $248.50  
  Purchase #5 $124.49   3.291%   $128.587   $128.59   $128.60   $128.60  
  Purchase #6 $249.76   5.468%   $263.4169   $263.42   $263.40   $263.40  
  Purchase #7 $38.78   13.412%   $43.9812   $43.98   $44.00   $44.00  
  7 purchase totals = $1,143.19       $1,234.6271   $1,234.63   $1,234.65   $1,234.60