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 $249.83   5.238%   $262.9161   $262.92   $262.90   $262.90  
  Purchase #2 $156.35   9.824%   $171.7098   $171.71   $171.70   $171.70  
  Purchase #3 $20.35   5.363%   $21.4414   $21.44   $21.45   $21.40  
  Purchase #4 $131.56   13.617%   $149.4745   $149.47   $149.45   $149.50  
  Purchase #5 $36.74   4.364%   $38.3433   $38.34   $38.35   $38.30  
  Purchase #6 $243.72   10.619%   $269.6006   $269.60   $269.60   $269.60  
  Purchase #7 $33.82   7.334%   $36.3004   $36.30   $36.30   $36.30  
  7 purchase totals = $872.37       $949.7861   $949.78   $949.75   $949.70