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 $177.94   13.671%   $202.2662   $202.27   $202.25   $202.30  
  Purchase #2 $69.46   10.354%   $76.6519   $76.65   $76.65   $76.70  
  Purchase #3 $19.28   12.168%   $21.626   $21.63   $21.65   $21.60  
  Purchase #4 $171.28   6.435%   $182.3019   $182.30   $182.30   $182.30  
  Purchase #5 $36.52   5.364%   $38.4789   $38.48   $38.50   $38.50  
  Purchase #6 $7.28   4.440%   $7.6032   $7.60   $7.60   $7.60  
  Purchase #7 $6.75   8.741%   $7.34   $7.34   $7.35   $7.30  
  7 purchase totals = $488.51       $536.2681   $536.27   $536.30   $536.30