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 $56.25   3.494%   $58.2154   $58.22   $58.20   $58.20  
  Purchase #2 $236.83   11.245%   $263.4615   $263.46   $263.45   $263.50  
  Purchase #3 $211.43   4.637%   $221.234   $221.23   $221.25   $221.20  
  Purchase #4 $115.92   6.147%   $123.0456   $123.05   $123.05   $123.00  
  Purchase #5 $186.60   3.775%   $193.6442   $193.64   $193.65   $193.60  
  Purchase #6 $168.75   11.427%   $188.0331   $188.03   $188.05   $188.00  
  Purchase #7 $78.69   10.732%   $87.135   $87.14   $87.15   $87.10  
  7 purchase totals = $1,054.47       $1,134.7688   $1,134.77   $1,134.80   $1,134.60