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 $64.32   6.243%   $68.3355   $68.34   $68.35   $68.30  
  Purchase #2 $130.26   10.594%   $144.0597   $144.06   $144.05   $144.10  
  Purchase #3 $211.50   6.626%   $225.514   $225.51   $225.50   $225.50  
  Purchase #4 $8.29   9.201%   $9.0528   $9.05   $9.05   $9.10  
  Purchase #5 $155.95   4.507%   $162.9787   $162.98   $163.00   $163.00  
  Purchase #6 $207.83   12.792%   $234.4156   $234.42   $234.40   $234.40  
  Purchase #7 $164.56   7.198%   $176.405   $176.41   $176.40   $176.40  
  7 purchase totals = $942.71       $1,020.7613   $1,020.77   $1,020.75   $1,020.80