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 $46.91   10.319%   $51.7506   $51.75   $51.75   $51.80  
  Purchase #2 $232.72   12.721%   $262.3243   $262.32   $262.30   $262.30  
  Purchase #3 $185.48   11.106%   $206.0794   $206.08   $206.10   $206.10  
  Purchase #4 $125.55   4.627%   $131.3592   $131.36   $131.35   $131.40  
  Purchase #5 $232.78   13.784%   $264.8664   $264.87   $264.85   $264.90  
  Purchase #6 $237.87   4.177%   $247.8058   $247.81   $247.80   $247.80  
  Purchase #7 $240.75   4.329%   $251.1721   $251.17   $251.15   $251.20  
  7 purchase totals = $1,302.06       $1,415.3578   $1,415.36   $1,415.30   $1,415.50