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 $64.96   3.374%   $67.1518   $67.15   $67.15   $67.20  
  Purchase #2 $243.95   3.693%   $252.9591   $252.96   $252.95   $253.00  
  Purchase #3 $232.77   12.217%   $261.2075   $261.21   $261.20   $261.20  
  Purchase #4 $208.90   4.270%   $217.82   $217.82   $217.80   $217.80  
  Purchase #5 $100.43   7.308%   $107.7694   $107.77   $107.75   $107.80  
  Purchase #6 $71.64   13.279%   $81.1531   $81.15   $81.15   $81.20  
  Purchase #7 $218.96   12.422%   $246.1592   $246.16   $246.15   $246.20  
  7 purchase totals = $1,141.61       $1,234.2201   $1,234.22   $1,234.15   $1,234.40