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 $246.74   10.620%   $272.9438   $272.94   $272.95   $272.90  
  Purchase #2 $208.39   4.444%   $217.6509   $217.65   $217.65   $217.70  
  Purchase #3 $247.49   3.422%   $255.9591   $255.96   $255.95   $256.00  
  Purchase #4 $85.45   13.473%   $96.9627   $96.96   $96.95   $97.00  
  Purchase #5 $176.87   12.326%   $198.671   $198.67   $198.65   $198.70  
  Purchase #6 $54.64   10.285%   $60.2597   $60.26   $60.25   $60.30  
  Purchase #7 $109.51   10.461%   $120.9658   $120.97   $120.95   $121.00  
  7 purchase totals = $1,129.09       $1,223.4130   $1,223.41   $1,223.35   $1,223.60