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 $151.41   6.861%   $161.7982   $161.80   $161.80   $161.80  
  Purchase #2 $113.87   11.539%   $127.0095   $127.01   $127.00   $127.00  
  Purchase #3 $169.88   10.684%   $188.03   $188.03   $188.05   $188.00  
  Purchase #4 $211.88   11.783%   $236.8458   $236.85   $236.85   $236.80  
  Purchase #5 $53.29   13.496%   $60.482   $60.48   $60.50   $60.50  
  Purchase #6 $11.55   4.599%   $12.0812   $12.08   $12.10   $12.10  
  Purchase #7 $209.42   13.868%   $238.4624   $238.46   $238.45   $238.50  
  7 purchase totals = $921.30       $1,024.7091   $1,024.71   $1,024.75   $1,024.70