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 $45.80   12.503%   $51.5264   $51.53   $51.55   $51.50  
  Purchase #2 $233.64   3.867%   $242.6749   $242.67   $242.65   $242.70  
  Purchase #3 $106.28   11.208%   $118.1919   $118.19   $118.20   $118.20  
  Purchase #4 $248.81   5.621%   $262.7956   $262.80   $262.80   $262.80  
  Purchase #5 $122.65   9.286%   $134.0393   $134.04   $134.05   $134.00  
  Purchase #6 $200.85   11.693%   $224.3354   $224.34   $224.35   $224.30  
  Purchase #7 $34.32   9.256%   $37.4967   $37.50   $37.50   $37.50  
  7 purchase totals = $992.35       $1,071.0602   $1,071.07   $1,071.10   $1,071.00