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 $214.77   11.458%   $239.3783   $239.38   $239.40   $239.40  
  Purchase #2 $187.69   8.576%   $203.7863   $203.79   $203.80   $203.80  
  Purchase #3 $158.64   11.351%   $176.6472   $176.65   $176.65   $176.60  
  Purchase #4 $170.98   7.771%   $184.2669   $184.27   $184.25   $184.30  
  Purchase #5 $53.52   12.791%   $60.3657   $60.37   $60.35   $60.40  
  Purchase #6 $31.82   9.110%   $34.7188   $34.72   $34.70   $34.70  
  Purchase #7 $166.76   5.822%   $176.4688   $176.47   $176.45   $176.50  
  7 purchase totals = $984.18       $1,075.6320   $1,075.65   $1,075.60   $1,075.70