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 $64.48   5.389%   $67.9548   $67.95   $67.95   $68.00  
  Purchase #2 $241.99   6.475%   $257.6589   $257.66   $257.65   $257.70  
  Purchase #3 $238.41   11.415%   $265.6245   $265.62   $265.60   $265.60  
  Purchase #4 $61.34   5.272%   $64.5738   $64.57   $64.55   $64.60  
  Purchase #5 $167.58   12.234%   $188.0817   $188.08   $188.10   $188.10  
  Purchase #6 $100.80   8.249%   $109.115   $109.12   $109.10   $109.10  
  Purchase #7 $127.81   5.434%   $134.7552   $134.76   $134.75   $134.80  
  7 purchase totals = $1,002.41       $1,087.7639   $1,087.76   $1,087.70   $1,087.90