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 $165.81   3.433%   $171.5023   $171.50   $171.50   $171.50  
  Purchase #2 $91.76   4.545%   $95.9305   $95.93   $95.95   $95.90  
  Purchase #3 $135.77   12.284%   $152.448   $152.45   $152.45   $152.40  
  Purchase #4 $182.81   12.204%   $205.1201   $205.12   $205.10   $205.10  
  Purchase #5 $87.88   11.342%   $97.8473   $97.85   $97.85   $97.80  
  Purchase #6 $199.51   13.412%   $226.2683   $226.27   $226.25   $226.30  
  Purchase #7 $119.92   5.444%   $126.4484   $126.45   $126.45   $126.40  
  7 purchase totals = $983.46       $1,075.5649   $1,075.57   $1,075.55   $1,075.40