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 $167.37   7.236%   $179.4809   $179.48   $179.50   $179.50  
  Purchase #2 $185.94   13.789%   $211.5793   $211.58   $211.60   $211.60  
  Purchase #3 $170.58   13.551%   $193.6953   $193.70   $193.70   $193.70  
  Purchase #4 $72.31   5.819%   $76.5177   $76.52   $76.50   $76.50  
  Purchase #5 $192.74   13.553%   $218.8621   $218.86   $218.85   $218.90  
  Purchase #6 $67.85   4.192%   $70.6943   $70.69   $70.70   $70.70  
  Purchase #7 $121.44   4.119%   $126.4421   $126.44   $126.45   $126.40  
  7 purchase totals = $978.23       $1,077.2717   $1,077.27   $1,077.30   $1,077.30