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 $59.99   12.715%   $67.6177   $67.62   $67.60   $67.60  
  Purchase #2 $110.97   3.171%   $114.4889   $114.49   $114.50   $114.50  
  Purchase #3 $139.50   4.464%   $145.7273   $145.73   $145.75   $145.70  
  Purchase #4 $214.28   8.309%   $232.0845   $232.08   $232.10   $232.10  
  Purchase #5 $174.61   3.849%   $181.3307   $181.33   $181.35   $181.30  
  Purchase #6 $110.59   5.471%   $116.6404   $116.64   $116.65   $116.60  
  Purchase #7 $85.51   12.446%   $96.1526   $96.15   $96.15   $96.20  
  7 purchase totals = $895.45       $954.0421   $954.04   $954.10   $954.00