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 $38.34   5.756%   $40.5469   $40.55   $40.55   $40.50  
  Purchase #2 $193.26   12.104%   $216.6522   $216.65   $216.65   $216.70  
  Purchase #3 $211.37   4.791%   $221.4967   $221.50   $221.50   $221.50  
  Purchase #4 $152.34   7.156%   $163.2415   $163.24   $163.25   $163.20  
  Purchase #5 $69.58   4.850%   $72.9546   $72.95   $72.95   $73.00  
  Purchase #6 $214.84   11.159%   $238.814   $238.81   $238.80   $238.80  
  Purchase #7 $234.99   8.446%   $254.8373   $254.84   $254.85   $254.80  
  7 purchase totals = $1,114.72       $1,208.5432   $1,208.54   $1,208.55   $1,208.50