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 $85.95   5.821%   $90.9531   $90.95   $90.95   $91.00  
  Purchase #2 $234.28   8.537%   $254.2805   $254.28   $254.30   $254.30  
  Purchase #3 $110.83   3.132%   $114.3012   $114.30   $114.30   $114.30  
  Purchase #4 $142.75   3.186%   $147.298   $147.30   $147.30   $147.30  
  Purchase #5 $165.27   13.557%   $187.6757   $187.68   $187.70   $187.70  
  Purchase #6 $9.48   12.666%   $10.6807   $10.68   $10.70   $10.70  
  Purchase #7 $196.27   9.406%   $214.7312   $214.73   $214.75   $214.70  
  7 purchase totals = $944.83       $1,019.9204   $1,019.92   $1,020.00   $1,020.00