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 $183.31   7.831%   $197.665   $197.67   $197.65   $197.70  
  Purchase #2 $43.47   3.635%   $45.0501   $45.05   $45.05   $45.10  
  Purchase #3 $202.67   10.267%   $223.4781   $223.48   $223.50   $223.50  
  Purchase #4 $160.34   10.238%   $176.7556   $176.76   $176.75   $176.80  
  Purchase #5 $197.36   4.754%   $206.7425   $206.74   $206.75   $206.70  
  Purchase #6 $134.31   4.841%   $140.8119   $140.81   $140.80   $140.80  
  Purchase #7 $239.42   12.520%   $269.3954   $269.40   $269.40   $269.40  
  7 purchase totals = $1,160.88       $1,259.8986   $1,259.91   $1,259.90   $1,260.00