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 $233.49   12.336%   $262.2933   $262.29   $262.30   $262.30  
  Purchase #2 $33.73   12.646%   $37.9955   $38.00   $38.00   $38.00  
  Purchase #3 $190.75   5.476%   $201.1955   $201.20   $201.20   $201.20  
  Purchase #4 $22.25   11.775%   $24.8699   $24.87   $24.85   $24.90  
  Purchase #5 $233.30   7.826%   $251.5581   $251.56   $251.55   $251.60  
  Purchase #6 $157.31   10.236%   $173.4123   $173.41   $173.40   $173.40  
  Purchase #7 $238.40   4.581%   $249.3211   $249.32   $249.30   $249.30  
  7 purchase totals = $1,109.23       $1,200.6457   $1,200.65   $1,200.60   $1,200.70