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 $120.39   5.429%   $126.926   $126.93   $126.95   $126.90  
  Purchase #2 $63.35   7.808%   $68.2964   $68.30   $68.30   $68.30  
  Purchase #3 $168.59   4.218%   $175.7011   $175.70   $175.70   $175.70  
  Purchase #4 $216.62   11.566%   $241.6743   $241.67   $241.65   $241.70  
  Purchase #5 $183.73   13.371%   $208.2965   $208.30   $208.30   $208.30  
  Purchase #6 $232.78   4.147%   $242.4334   $242.43   $242.45   $242.40  
  Purchase #7 $210.93   13.762%   $239.9582   $239.96   $239.95   $240.00  
  7 purchase totals = $1,196.39       $1,303.2859   $1,303.29   $1,303.30   $1,303.30