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 $230.30   13.603%   $261.6277   $261.63   $261.65   $261.60  
  Purchase #2 $181.79   5.770%   $192.2793   $192.28   $192.30   $192.30  
  Purchase #3 $239.34   13.834%   $272.4503   $272.45   $272.45   $272.50  
  Purchase #4 $216.51   11.157%   $240.666   $240.67   $240.65   $240.70  
  Purchase #5 $46.84   12.430%   $52.6622   $52.66   $52.65   $52.70  
  Purchase #6 $184.90   9.747%   $202.9222   $202.92   $202.90   $202.90  
  Purchase #7 $95.75   13.558%   $108.7318   $108.73   $108.75   $108.70  
  7 purchase totals = $1,195.43       $1,331.3395   $1,331.34   $1,331.35   $1,331.40