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 $203.35   11.538%   $226.8125   $226.81   $226.80   $226.80  
  Purchase #2 $191.80   10.874%   $212.6563   $212.66   $212.65   $212.70  
  Purchase #3 $190.58   9.292%   $208.2887   $208.29   $208.30   $208.30  
  Purchase #4 $18.75   3.312%   $19.371   $19.37   $19.35   $19.40  
  Purchase #5 $170.65   3.286%   $176.2576   $176.26   $176.25   $176.30  
  Purchase #6 $175.26   12.854%   $197.7879   $197.79   $197.80   $197.80  
  Purchase #7 $20.65   7.342%   $22.1661   $22.17   $22.15   $22.20  
  7 purchase totals = $971.04       $1,063.3401   $1,063.35   $1,063.30   $1,063.50