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 $58.88   7.294%   $63.1747   $63.17   $63.15   $63.20  
  Purchase #2 $198.49   5.426%   $209.2601   $209.26   $209.25   $209.30  
  Purchase #3 $186.51   4.342%   $194.6083   $194.61   $194.60   $194.60  
  Purchase #4 $127.37   10.705%   $141.005   $141.01   $141.00   $141.00  
  Purchase #5 $119.71   12.582%   $134.7719   $134.77   $134.75   $134.80  
  Purchase #6 $37.87   11.541%   $42.2406   $42.24   $42.25   $42.20  
  Purchase #7 $116.37   4.453%   $121.552   $121.55   $121.55   $121.60  
  7 purchase totals = $845.20       $906.6126   $906.61   $906.55   $906.70