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 $243.41   10.628%   $269.2796   $269.28   $269.30   $269.30  
  Purchase #2 $30.88   13.186%   $34.9518   $34.95   $34.95   $35.00  
  Purchase #3 $168.71   7.521%   $181.3987   $181.40   $181.40   $181.40  
  Purchase #4 $146.52   9.164%   $159.9471   $159.95   $159.95   $159.90  
  Purchase #5 $164.47   4.707%   $172.2116   $172.21   $172.20   $172.20  
  Purchase #6 $185.80   4.126%   $193.4661   $193.47   $193.45   $193.50  
  Purchase #7 $59.88   7.550%   $64.4009   $64.40   $64.40   $64.40  
  7 purchase totals = $999.67       $1,075.6558   $1,075.66   $1,075.65   $1,075.70